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# need help.. Can't find a solution

Implement the Subtract method so that the test passes.

Calculator.cs
```public class Calculator
{
public double Result;

public Calculator(double number)
{
Result = number;
}

{
Result += number;
}

public void Substract(double number)
{
Result -= number;
}
}
```
CalculatorTests.cs
```using Xunit;

public class CalculatorTests
{
[Fact]
public void Initialization()
{
var expected = 1.1;
var target = new Calculator(1.1);
Assert.Equal(expected, target.Result, 1);
}

[Fact]
{
var target = new Calculator(1.1);
var expected = 3.3;
Assert.Equal(expected, target.Result, 1);
}

[Fact]
public void BasicSubtract()
{
var target = new Calculator(1.1);
target.Subtract(0.2);
var expected = 0.9;
Assert.Equal(expected, target.Result, 1);
}
}
```

You're really close, but you you have a little spelling/typo error.

You have "Substract" (with an extra "s") instead of "Subtract".

PLUS

Can someone please explain what the last parameter (1) does in this piece of code Assert.Equal(expected, target.Result, 1);.

I have looked at the documentation and found only two object passed in as the parameter.

https://docs.microsoft.com/en-us/dotnet/api/microsoft.visualstudio.testtools.unittesting.assert.equals?view=mstest-net-1.2.0