a man swims downstream 72 km and upstream 45 km taking 6 hours each time ; what is the speed of the current ?
"72 - - - 6 ds = 12 ? - - - - 1 45 - - - - 6 us = 7.5 ? - - - - 1 s = ? s = ( 12 - 7.5 ) / 2 = 2.25 answer : d"
divide(add(divide(45, 6), divide(72, 6)), const_2)