A man can swim in still water at 12 km/h, but takes twice as long to swim upstream than downstream. The speed of the stream is?  Select the correct option.
A) 1.7  B) 2.67  C) 1.2  D) 1.5  E) 4

Rationale: "m = 12 s = x ds = 12 + x us = 12 + x 12 + x = ( 12 - x ) 2 12 + x = 24 - 2 x 3 x = 12 x = 4 answer : e"
Answer: E