Rosy waxes 2/3 of her car with 1/4 bottle of car wax. At this rate, what fraction of the bottle of car wax will Rosy use to wax her entire car?

A: 1/8

B: 1/6

C: 3/8

D: 3/4

(2/3) / (1/4) = 1 / x ... 2/3 of car to 1/4 car wax = 1 car to x car wax

cross multiply

(2/3) (x) = (1/4) (1)

2/3x = 1/4

x = (1/4) / (2/3)

x = 1/4 * 3/2

x = 3/8 bottle of car wax <==