diff --git a/Lesson_6/Task_1/Classes/Calculator.cs b/Lesson_6/Task_1/Classes/Calculator.cs
new file mode 100644
index 0000000..e251d12
--- /dev/null
+++ b/Lesson_6/Task_1/Classes/Calculator.cs
@@ -0,0 +1,58 @@
+namespace Lesson6.Classes;
+
+using Lesson6.Interfaces;
+
+public class Calculator : ICalculator
+{
+    public event ICalculator.CalculationPerformedEventHandler? CalculationPerformed;
+
+    public void Calculate(string expression)
+    {
+        string[] tokens = expression.Split(' ');
+
+        double firstNumber;
+        double secondNumber;
+        string inputOperation;
+        double result;
+        Operation operation = new Operation();
+        Operation.Do oper;
+
+        try
+        {
+            firstNumber = double.Parse(tokens[0]);
+            secondNumber = double.Parse(tokens[2]);
+            inputOperation = tokens[1];
+        }
+        catch
+        {
+            Console.WriteLine("Invalid format.");
+            return;
+        }
+
+        switch (inputOperation)
+        {
+            case "+":
+                oper = operation.Add;
+                break;
+            case "-":
+                oper = operation.Subtract;
+                break;
+            case "*":
+                oper = operation.Multiply;
+                break;
+            case "/":
+                oper = operation.Divide;
+                break;
+            default:
+                Console.WriteLine("Invalid operation.");
+                return;
+        }
+
+        result = oper.Invoke(firstNumber, secondNumber);
+
+        // raise the event
+        CalculationPerformed?.Invoke(result);
+    }
+
+    public delegate void CalculationPerformedEventHandler(double result);
+}
diff --git a/Lesson_6/Task_1/Classes/Operation.cs b/Lesson_6/Task_1/Classes/Operation.cs
new file mode 100644
index 0000000..e04eec4
--- /dev/null
+++ b/Lesson_6/Task_1/Classes/Operation.cs
@@ -0,0 +1,12 @@
+namespace Lesson6.Classes;
+
+using Lesson6.Interfaces;
+
+public class Operation : IOperation
+{
+    public double Add(double firstSummand, double secondSummand) => firstSummand + secondSummand;
+    public double Subtract(double minuend, double subtrahend) => minuend - subtrahend;
+    public double Multiply(double firstFactor, double secondFactor) => firstFactor * secondFactor;
+    public double Divide(double dividend, double divisor) => dividend / divisor;
+    public delegate double Do(double firstNumber, double secondNumber);
+}
diff --git a/Lesson_6/Task_1/Interfaces/ICalculator.cs b/Lesson_6/Task_1/Interfaces/ICalculator.cs
new file mode 100644
index 0000000..f07be51
--- /dev/null
+++ b/Lesson_6/Task_1/Interfaces/ICalculator.cs
@@ -0,0 +1,10 @@
+namespace Lesson6.Interfaces;
+
+public interface ICalculator
+{
+    event CalculationPerformedEventHandler? CalculationPerformed;
+
+    void Calculate(string expression);
+
+    delegate void CalculationPerformedEventHandler(double result);
+}
diff --git a/Lesson_6/Task_1/Interfaces/IOperation.cs b/Lesson_6/Task_1/Interfaces/IOperation.cs
new file mode 100644
index 0000000..6c29e07
--- /dev/null
+++ b/Lesson_6/Task_1/Interfaces/IOperation.cs
@@ -0,0 +1,10 @@
+namespace Lesson6.Interfaces;
+
+public interface IOperation
+{
+    double Add(double firstSummand, double secondSummand);
+    double Subtract(double minuend, double subtrahend);
+    double Multiply(double firstFactor, double secondFactor);
+    double Divide(double dividend, double divisor);
+    delegate double Do(double x, double y);
+}
diff --git a/Lesson_6/Task_1/Program.cs b/Lesson_6/Task_1/Program.cs
new file mode 100644
index 0000000..c5d393d
--- /dev/null
+++ b/Lesson_6/Task_1/Program.cs
@@ -0,0 +1,29 @@
+using Lesson6.Classes;
+
+namespace Lesson6
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            Calculator calc = new Calculator();
+
+            // subscribe to the event
+            calc.CalculationPerformed += result => Console.WriteLine($"Result: {result}");
+
+            while (true)
+            {
+                Console.Write("Enter expression (e.g. 2 + 2) or exit: ");
+                string? expression = Console.ReadLine();
+
+                if (expression == null)
+                    continue;
+
+                if (expression == "exit")
+                    break;
+
+                calc.Calculate(expression);
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/Lesson_6/Task_1/Task_1.csproj b/Lesson_6/Task_1/Task_1.csproj
new file mode 100644
index 0000000..74abf5c
--- /dev/null
+++ b/Lesson_6/Task_1/Task_1.csproj
@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>