200 miles were driven if the cost is $130.
To solve, identify what each part of the equation means, plug 130 into the right part of the equation, and solve for m.
C(M) ⇒ Cost for renting a car
0.50M ⇒ Cost per mile driven
M ⇒ Miles driven
30 ⇒ Initial cost
Replace C(M) with 130 and solve for M.
130 = 0.50M + 30
100 = 0.50M
200 = M
So, if the cost is $130, 200 miles were driven.