Swift - How to use user input in func with if-statement to decide output

I've been trying to write a function that takes user input and then returns the correct output in the textfield of my app, but can't get output.

What I have so far:

func outputResult (weeksNumber: Int, hoursNumber: Int) {

    let weeksNumber = Int(weeksNumber)
    let hoursNumber = Int(hoursNumber)

   let result1 = "test1" 
    let result2 = "test2"
    let result3 = "test3"

    if hoursNumber < 74 {
        resultText.text = result1 // ResultText being my textfield.
    } else if weeksNumber < 8 {
        resultText.text = result2
    } else {
        resultText.text = result3
    }
}

I've been trying to go through Apple's own material on functions and if-statements, but haven't been able to figure out how to do exactly what I want.

I've been trying out with:

func outputResult (weeksNumber: Int, hoursNumber: Int) - String {

    let weeksNumber = Int(weeksNumber)
    let hoursNumber = Int(hoursNumber)


    if hoursNumber < 74 {
        return resultText.text = "test1" 
    }

But this also doesn't solve my problem - merely giving me an error message.

My question is : How do I get my function to take user input and return output to my textfield?

Cheers,