Missing argument label when calling a method in "strategy design pattern" -SWIFT

I am recently venture myself into Swift but I could not understand why my codes does not work when im returning an Int in a method.

protocol StrategyProtocol
{
    func calculate(num1:Int, num2:Int) ->Int
}

class Context
{
    var _strategyProtocol: StrategyProtocol!

    init(_strategyProtocol: StrategyProtocol)
    {
        self._strategyProtocol=_strategyProtocol
    }

    func Calculate(num1: Int, num2: Int) ->Int
    {
        return _strategyProtocol.calculate(num1, num2)
    }
}

class Add: StrategyProtocol
{
    func calculate(num1: Int, num2: Int) -> Int
    {
        return num1 + num2
    }
}

class Minus: StrategyProtocol
{
    func calculate(num1: Int, num2: Int) -> Int
    {
        return num1 - num2
    }
}

apparently this line of code does not work and prompt out missing argument label 'num2:' in call

//return _strategyProtocol.calculate(num1, num2)

can anyone show me how to fix it and explain to me.