Write a Cost Function for the Problem $\$ 55$ Plus $\$ 40$

Multiple Choice

Write a cost function for the problem. Assume that the relationship is linear.
-An electrician charges a fee of $\$ 55$ plus $\$ 40$ per hour. Let $C(x)$ be the cost in dollars of using the electrician for $x$ hours.

A) $C(x) =55 x-40$
B) $C(x) =40 x-55$
C) $C(x) =40 x+55$
D) $C(x) =55 x+40$