water is emptied from a water tank using a tap at its base. The depth of the water in the tank, d cm, can be modelled by the function

\(\displaystyle

d(t) = (((t-150)^2)/1000)+1

\)

a) show it can be written as

d(t)=0.001t^2 - 0.3t + 23.5

b) find value of d'(80)

any help would be appreciated, im really stuck. even just an explination of how to go about this.