excluding stoppages , the speed of a bus is 54 km / hr and including stoppages , it is 45 km / hr . for how many minutes does the bus stop per hour ?
"due to stoppages , it covers 9 km less . time taken to cover 9 km = 9 / 54 * 60 = 10 min . answer : b"
multiply(const_60, divide(subtract(54, 45), 54))