A program contains the statement tax = calcTax(sales);. The tax and sales variables have...

A program contains the statement tax = calcTax(sales);. The tax and sales variables have the double data type. Which of the following is a valid function header for the calcTax function?

a. calcTax(double sales);

b. double calcTax(salesAmount)

c. double calcTax(double salesAmount)

d. double calcTax(int sales);