When x=-1: [tex]\quad (-1)y=-4\qquad\to\qquad y=4\)[/tex]
Ok that gives us a little more information.
If we implicitly differentiate with respect to t, from the very start, then we can apply our product rule, ya?
[tex]x'y+xy'=0[/tex]
The right side is zero, derivative of a constant is zero.
Where x' is dx/dt and y' is dy/dt.
From here, plug in all the stuff you know:
y' = -3
x = -1
y = 4
and solve for x'.
Hope that helps!
