Problem: a man can row his boat with the stream at 12 km / h and against the stream in 8 km / h . the man ' s rate is ?
Rationale: explanation : ds = 12 us = 8 s = ? s = ( 12 - 8 ) / 2 = 2 kmph answer : a
annotated_formula: divide(subtract(12, 8), const_2)