51 persons can repair a road in 12 days, working 5 hours a day. In how many days will 30 persons, working 6 hours a day, complete the work?	Pick:
A) 10 B) 13 C) 14 D) 15 E) 17

Rationale: "according to the chain rule , m 1 x t 1 = m 2 x t 2 therefore , 51 x 12 x 5 = 30 x 6 x x x = 17 hence , the number of days = 17 . answer : e"
Answer: E