Question from the Language C - Fundamentals test

What parameter is used in the main?

double annualSalary(double monthlySalary);
double increase(double annualSalary);
void prime(double monthlySalary); 
    
    int main() 
    {
        prime(1298.75);
        return 0;
    }
    
    double annualSalary( double monthlySalary) {
        return monthlySalary *= 12;
    }

    double increase(double annualSalary){
        return 1.1*annualSalary;
    }

    void prime(double monthlySalary){
        double annualRevenue = annualSalary(monthlySalary);
        printf("your salary increases from %f euros to %f euros",annualRevenue,increase(annualRevenue));
    }