Determine Whether or Not the Function Is Linear $C ( x ) = 137 + 0.25 x$

Determine whether or not the function is linear. If it is, determine the slope and interpret it.
-The cost of a rental car for the weekend is given by the function C(x) $C ( x ) = 137 + 0.25 x$ , where x is the number of miles driven. Find and interpret the C-intercept of the graph of this function.

A) 137; The cost of the rental car increases by $137 for each mile driven.
B) 0.25; The cost of the rental car increases by $0.25 for each mile driven.
C) 137; There is a flat rate of $137 to rent a car in addition to the charge for each mile driven.
D) 0.25; There is a flat rate of $0.25 to rent a car in addition to the charge for each mile driven.