Solve the given problems by finding the appropriate derivative.
The electric power $P$ (in $\mathrm{W}$ ) as a function of the current $i$ (in $\mathrm{A}$ ) in a certain circuit is given by $P=16 i^{2}+60 i .$ Find the instantaneous rate of change of $P$ with respect to $i$ for $i=0.75 A$.