A can work four times as fast as B. Together they can finish a job in 10 days. In how many days can A complete the job alone?
Choose the correct choice from the following choices:
A) 11.5  B) 12.5  C) 13.5  D) 14.5  E) 15.5
B's rate is x and A's rate is 4x.   x + 4x = 1/10   x = 1/50   A's rate is 4x = 1/12.5   A can complete the job in 12.5 days.   The answer is 12.5.
<result>B</result>
A can work four times as fast as B. Together they can finish a job in 10 days. In how many days can A complete the job alone?