a man can swim in still water at 9 km / h , but takes twice as long to swim upstream than downstream . the speed of the stream is ?
"m = 9 s = x ds = 9 + x us = 9 - x 9 + x = ( 9 - x ) 2 9 + x = 18 - 2 x 3 x = 9 x = 3 answer : c"
divide(9, const_3)