A bolt is dropped from a bridge under construction, falling 81 m to the valley below…

A bolt is dropped from a bridge under construction, falling 81 m
to the valley below the bridge. (a) How much time
does it take to pass through the last 30 % of its fall? What is its
speed (b) when it begins that last 30 % of its
fall and (c) just before it reaches the
ground?