I have two different questions

my first one is differentiate with respect to t

y=x^2-3x find dy/dt when x=3 and dx/dt=2

This is what I did

dy/dt=2x (dx/dt)-3 I am not sure if this is correct

my second one is

xy=4 find dy/dt when x=8 dx/dt=10

I am not sure how to begin this one