a boat goes 130 km downstream in 10 hours , and 75 km upstream in 15 hours . the speed of the stream is ?
"125 - - - 10 ds = 130 ? - - - - 1 75 - - - - 15 us = 5 ? - - - - - 1 s = ( 13 - 5 ) / 2 = 4 kmph . answer : d"
divide(subtract(divide(130, 10), divide(75, 15)), const_2)