Answer:
The option B is correct, i.e. 6 mph.
Step-by-step explanation:
Suppose Samantha swim in still water at speed of X mph.
If the river flows at 4 mph,
Then Upstream speed = (X-4) mph.
And Downstream speed = (X+4) mph.
Samantha swam upstream for some distance in one hour. She then swam downstream the same river for the same distance in only 12 minutes.
It means <u>Distance upstream = Distance downstream</u>.
Speed upstream x Time upstream = Speed downstream x Time downstream.
(x-4) * 1 = (x+4) * 12/60
x - 4 = 0.2x + 0.8
x - 0.2x = 0.8 + 4
0.8x = 4.8
x = 4.8/0.8 = 6 mph.
Hence, the option B is correct, i.e. 6 mph.
