a boy swims downstream 56 km and upstream 42 km taking 7 hours each time ; what is the speed of the current ?
"56 - - - 7 ds = 8 ? - - - - 1 42 - - - - 7 us = 6 ? - - - - 1 s = ? s = ( 8 - 6 ) / 2 = 1 answer : e"
multiply(divide(const_1, const_2), add(divide(56, 7), divide(42, 7)))