Hey everyone, I just took the GMAT and you won't believe it but this question actually appeared (I got a 48 on the quant 85%). Luckly for me it was the second to last question, I recognized the question from before and happened to know the answer. How would you really solve this question.

Considering a semicircular cross section of a one-way tunnel with a diameter of 20 feet. The single traffic lane is 12 feet wide and is equidistant from the sides of the tunnel. If vehicles must clear the top of the tunnel by at least 1/2 foot when they are inside the traffic lane, what should be the limit on the height of vehicles that are allowed to use the tunnel?

A. 5 1/2 ft

B. 7 1/2 ft

C. 8 1/2 ft

D. 9 1/2 ft

E. 10 ft

Thank everyone.