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 ?
"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 ."
divide(multiply(multiply(30, divide(6, 7)), inverse(subtract(const_1, divide(6, 7)))), const_60)