a man whose speed is 3 kmph in still water rows to a certain upstream point and back to the starting point in a river which flows at 1.5 kmph , find his average speed for the total journey ?
"m = 3 s = 1.5 ds = 4.5 us = 3 as = ( 2 * 4.5 * 3 ) / 7.5 = 3.6 answer : e"
divide(add(3, subtract(3, 1.5)), const_2)