a man swims downstream 72 km and upstream 45 km taking 3 hours each time ; what is the speed of the current ?
"72 - - - 3 ds = 24 ? - - - - 1 45 - - - - 3 us = 15 ? - - - - 1 s = ? s = ( 24 - 15 ) / 2 = 4.5 answer : c"
divide(add(divide(45, 3), divide(72, 3)), const_2)