An equation relating the variables $x$ and $y,$ the values of $x$ and $y,$ and the value of $\frac{ax}{dt}$ at a particular instant of time are given. Find the value of $\frac{dy}{dt}.$

$x^{2}y=45$;$,x=-3,y=5,\frac{dx}{dt}=4$;$,\frac{dy}{dt}=$