excluding stoppages , the speed of a bus is 90 km / hr and including stoppages , it is 84 km / hr . for how many minutes does the bus stop per hour ?
"due to stoppages , it covers 6 km less . time taken to cover 6 km = 6 / 90 * 60 = 4 min . answer : b"
multiply(const_60, divide(subtract(90, 84), 90))