.
= 12xy
Differentiate, considering y as a function of x, y = y(x) :
3x^2 + 3y^2*y' = 12y + 12x*y'
Collect the terms with y' in one side; the terms with no y' in the other side :
3y^2*y' - 12x*y' = 12y - 3x^2
y'*(3y^2 - 12x) =
.
Express y' :
y' =
,
or, canceling the common factor 3 in the numerator and in the denominator,
y' =
,
It is your answer.