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Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today. # I cannot figure out how to add a method with a parameter of type double

I need to do the following: "We need to figure out the tax amount when the tax percentage is 7.5 percent. Call the method calculateTaxes on the variable item and assign the result to a new variable named taxes."

I have done the code that you see, but the coding challenge says that I need to add a method named calculateTaxes with a parameter named Percentage of type double. I'm not sure what I am doing wrong. If you could please help, that would be great!

struct.swift
```struct Expense {
var description: String
var amount: Double = 0.0

init (description: String) {
self.description = description
}

func calculateTaxes(parameter: Double, percentage: Double) -> Double  {
return (self.amount * (parameter/100))

}

}

var item = Expense(description: "Gas price")
item.amount = 100

var taxes = item.calculateTaxes(percentage)

// add the calculateTaxes method here
// it should accept only one parameter named 'percentage' of t
``` Hello Austin :

What’s is important here is that you are very close and seem to understand most of the concept of accessing a structs properties and such with the dot syntax.

Please see the 2 codes below, the first one is yours, and I will highlight with comments some changes, and the second code will give you those changes and the answer to your challenge.

```struct Expense {
var description: String
var amount: Double = 0.0

init (description: String) {
self.description = description
}

/*
The challenge says to create a method with a parameter named
“percentage” of type double. As you can see on your method,
you have an extra parameter.
(parameter: Double) should not be in the method’s signature.
*/

func calculateTaxes(parameter: Double, percentage: Double) -> Double  {
return (self.amount * (parameter/100))

}

}

var item = Expense(description: "Gas price")
item.amount = 100
/*
Since you have an extra parameter not required by the challenge,
then you don’t need to add (percentage) here. Instead use a 7.5 which is
what the challenge wanted for taxes.
*/

var taxes = item.calculateTaxes(percentage)
```

This is what you want :

```struct Expense {
var description: String
var amount: Double = 0.0

init (description: String) {
self.description = description
}

func calculateTaxes(percentage: Double) -> Double {
return (self.amount * (percentage / 100))

}

}

var item = Expense(description: "Gas Price" )
item.amount = 100

var taxes = item.calculateTaxes(7.5)

/*
You may be wondering, “Why did you not put item.calculateTaxes(percentage: 7.5)”
This is because the name of the parameter is not explicit. If you wanted to make

Examples:

on swift 1.2
func calculateTaxes(#percentage: Double) -> {}

on swift 2.0
func calculateTaxes(percentage percentage: Double) -> {}

*/
```

I hope that helps, if you have any other questions please ask :)

Happy learning