The amount of time that three people worked on a special project was in the ratio of 3 to 5 to 6. If the project took 140 hours, how many more hours did the hardest working person work than the person who worked the least?
Choose the correct option
A) 32 hours  B) 40 hours  C) 35 hours  D) 30 hours  E) 36 hours

Rationale: "let the persons be a , b , c . hours worked : a = 3 * 140 / 14 = 30 hours b = 5 * 140 / 14 = 50 hours c = 6 * 140 / 14 = 60 hours c is the hardest worker and a worked for the least number of hours . so the difference is 60 - 30 = 30 hours . answer : d"
Answer: D