Calculate Total Cost with Linear Equation

A diner offers a special deal where the total cost, $C$, of a meal consists of a base price of $12 plus $3 for each drink ordered. If a customer orders $d$ drinks, the relationship between the total cost and the number of drinks can be expressed by the equation:

C = 12 + 3d

What is the total cost for a meal if a customer orders 4 drinks?