P is three times as fast as Q and working together, they can complete a work in 42 days. In how many days can Q alone complete the work?	Choose the correct choice from the following.
A) 16
B) 77
C) 56
D) 55
E) 778
P = 3Q   P + Q = 3Q + Q = 4Q   These 4Q people can do the work in 42 days, which means Q can do the work in 168 days.   Hence, P can do the work in 56 days.   Answer:56
<result>C</result>
P is three times as fast as Q and working together, they can complete a work in 42 days. In how many days can Q alone complete the work?