2016 ONE(b)

The height of the tide at a particular beach today is given by the function

$h(t)=0.8\sin \left(\frac{4\pi }{25}t+\frac{\pi }{2}\right)$

where $h$ is the height of water, in metres, relative to the mean sea level
and $t$ is the time in hours after midnight.

At what rate was the height of the tide changing at that beach at 9.00 a.m. today?