If 3 machines can build a car in 12 hours, how fast can 4 machines do it?  Select the correct option.
A) 10 hours
B) 9 hours
C) 8 hours
D) 7 hours
E) 11 hours
3 * 12 = 4 * x   x = 9 hours   Answer: 9 hours
<result>B</result>
If 3 machines can build a car in 12 hours, how fast can 4 machines do it?