Marta’s fruit stand sold x oranges on Thursday and twice as many on Friday. All together, on both days, she sold 108. Which bar diagram represents the equation?

a bar diagram. The top box contains 108. The bottom boxes contain x and 2 x.
b bar diagram. The top box contains x. The bottom boxes contain 108 and 2 x.
c bar diagram. The top box contains 2 x. The bottom boxes contain x and 108.
d bar diagram. The top box contains 108 x. The bottom boxes contain x and 2.