gwd-2-6滔滔

Q6:The figure above shows the dimensions of a semicircular cross section of a one-way tunnel.  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 ½ 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.     5½ ft

B.     7½ ft

C.     8 ½ ft

D.     9½ ft

E.      10 ft

这个题不知道怎么解答，答案b,原来是个半圆形的图，直径给的20

6^2+(h+0.5)^2=10^2

[attachimg]48500[/attachimg]

thanks a lot