Finding $f_x$ and and $f_y$ in a $f(x,y)$ function.

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Let  $f(x,y)  =  x^4y + 6xy^3 + 3x^4$.

(a) Find  $f_x$.

(b) Find  $f_y$.

I believe that I should make the equation equal to the function that I am looking for to solve the question. Would I be able to find the answer this way, and if not, how should I?

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Let  $f(x,y)  =  x^4y + 6xy^3 + 3x^4$.

(a) We find $f_x$ by holding all the other variables (other than $x$) as constants. In this setting, we are holding $y$ as a constant. So we obtain: $f_x = f_x (x,y)= 4x^3 y + 6y^3 +12 x^3$.

(b) Similarly, $f_y = f_y(x,y)=x^4 +18xy^2$.