A train is moving at 6/7 of its usual speed. The train is 30 minutes too late. What is the usual time for the train to complete the journey?  Choose one
A) 1 hour  B) 30 minutes  C) 3 hours  D) 2 hours 30 min  E) 2 hours

Rationale: "new time = d / ( 6 v / 7 ) = 7 / 6 * usual time 30 minutes represents 1 / 6 of the usual time . the usual time is 3 hours . the answer is c ."
Answer: C