Spot the error

This Swift code contains one error – can you select the line that is incorrect?

Tip: You should mentally run the code from top to bottom, meaning that if line 3 says an integer should be returned and line 10 tries to return a string, line 10 is the wrong one.

func calculateWorkload(employees: Int) -> String {

    var calculation = employees * 10_000

    if employees > 10 {

        calculation += 20_000

    }

    let str: Int = "The result is \(calculation)"

    return str

}

print(calculateWorkload(employees: 8))