A man can swim in still water at 4.5 km/h, but takes twice as long to swim upstream than downstream. The speed of the stream is_________?

A. 3
B. 7.5
C. 2.25
D. 1.5

Explanation:

M = 4.5
S = x
DS = 4.5 + x
US = 4.5 + x
4.5 + x = (4.5 – x)2
4.5 + x = 9 -2x
3x = 4.5
x = 1.5