a man swims downstream 65 km and upstream 35 km taking 5 hours each time ; what is the speed of the current ?
"65 - - - 5 ds = 13 ? - - - - 1 35 - - - - 5 us = 7 ? - - - - 1 s = ? s = ( 13 - 7 ) / 2 = 3 answer : b"
divide(add(divide(35, 5), divide(65, 5)), const_2)