Related rates Calculus problem

Question

Suppose xy = 1 and dy/dt = -3. Find dx/dt when x = -4

Answer 1

Differentiation gives: xdy/dt + ydx/dt = 0;

If x = - 4 then y = -1/4. So, - 4·(- 3) - 1/4·dx/dt = 0; dx/dt = 48.