a man can swim in still water at 15 km / h , but takes twice as long to swim upstream than downstream . the speed of the stream is ?
"m = 15 s = x ds = 15 + x us = 15 - x 15 + x = ( 15 - x ) 2 15 + x = 30 - 2 x 3 x = 15 x = 5 answer : b"
divide(15, const_3)