Write a Cost Function for the Problem $\$ 30$ Plus $\$ 25$

Multiple Choice

Write a cost function for the problem. Assume that the relationship is linear.
-A moving firm charges a flat fee of $\$ 30$ plus $\$ 25$ per hour. Let $C(x)$ be the cost in dollars of using the moving firm for $x$ hours.

A) C $(\mathrm{x}) =30 \mathrm{x}-25$
B) $C(x) =25 x-30$
C) $C(x) =25 x+30$
D) $C(x) =30 x+25$