Swift 2.0 Function Parameter Names

Have trouble getting the concept. I thought I had this right but I am obviously very wrong. But I know I am on track, but think i am on the wrong train. can anyone get me going in the right direction.

In this task we're going to write a simple function that takes two numbers and returns the remainder of dividing one number by the other.

Step 1: Declare a function named getRemainder that takes two parameters, aand b, both of type Int, and returns the value, also of type Int, obtained by carrying out the operation a modulo b. In case you've forgotten, the modulo operator is also called the remainder operator.

Step 2: The local names of the parameters are convenient but they make it hard to figure out the meaning of the function when we call it. Add two external names - value, for the first parameter and divisor for the second.

I use this code and get this answer: Bummer! Make sure your function accepts two parameters, named a and b, of type Int with the correct external parameter names

func getRemainder(divisor a: Int,value b: Int) -> Int {

    return a % b
}