A parking lot charges $2 per hour for the first 4 hours, then $3 per hour after that. Which equation(s) describes the total cost y as a function of the hours x?
a) y = 3x + 8
b) y = 2x + 12
c) y = 2x for x of 4 or less / y = 2x + 3x for x of 5 or more
d) y = 2x for x of 4 or less / y = 8 + 3(x - 4) for x of 5 or more