Problem concerned to kinematics

[Mareena]

Homework Statement

A body standing on a bridge throws a stone vertically upwards with a velocity of 20 m/s. it strikes the water below after 3 seconds, the height of the bridge over the water level in the river is :
a. 45 m
b. 10 m
c. 5 m
d. 15 m

Homework Equations

vf^2= 2aS + vi^2

The Attempt at a Solution

its ans mentioned in key is 5m, but i dnt undrstand how !
The time taken to reach max height (h) is given by..
v = u - gt .. where v = 0 m/s
t = u/g .. .. 20m/s / 9.80m/s² = 2s ..

So it takes 2x2s (4s) to return to the position it was thrown from (on the bridge) .. yet the question gives a time 3s to reach the water below the bridge.

 

[Doc Al]

You're right. It makes no sense. (Must be an error in the problem statement.)