39 persons can repair a road in 12 days, working 10 hours a day. In how many days will 30 persons, working 6 hours a day, complete the work?	Select.
A) 10 B) 13 C) 14 D) 15 E) 26

Rationale: "let the required number of days be x . less persons , more days ( indirect proportion ) more working hours per day , less days ( indirect proportion ) persons 30 : 39 : : 12 : x working hours / day 6 : 10 30 x 6 x x = 39 x 10 x 12 x = ( 39 x 10 x 12 ) / ( 30 x 6 ) x = 26 . answer : e"
Answer: E