a train is moving at 6 / 7 of its usual speed . the train is 15 minutes too late . what is the usual time ( in hours ) for the train to complete the journey ?
"new time = d / ( 6 v / 7 ) = 7 / 6 * usual time 15 minutes represents 1 / 6 of the usual time . the usual time is 1.5 hours . the answer is b ."
divide(multiply(multiply(15, divide(6, 7)), inverse(subtract(const_1, divide(6, 7)))), const_60)