a man whose speed is 4 kmph in still water rows to a certain upstream point and back to the starting point in a river which flows at 1 kmph , find his average speed for the total journey ?
"m = 4 s = 1 ds = 5 us = 3 as = ( 2 * 5 * 3 ) / 8 = 3.75 answer : d"
divide(add(4, subtract(4, 1)), const_2)