Problem: a man whose speed is 6 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 ?
Rationale: "m = 6.0 s = 1.5 ds = 7.5 us = 4.5 as = ( 2 * 7.5 * 4.5 ) / 12 = 5.6 answer : b"
annotated_formula: divide(add(6, subtract(6, 1.5)), const_2)