Motion In A Plane

A horizontal bridge is built across a river. A student standing on the bridge throws a small ball vertically upwards with a velocity \(4 \mathrm{~m} \mathrm{~s}^{-1}\). The ball strikes the water surface after \(4 \mathrm{~s}\). The height of bridge above water surface is (Take \(g=10 \mathrm{~m} \mathrm{~s}^{-2}\) )