If f(x,y,z) = (x^3 + y^2 + z)^4 find each of the following:

a) fx(x,y,z)

b) fy(0,1,1)

c) fzz(x,y,z)

For a) I got 4(x^3 + y^2 + z)(3x^2)

b) 4(x^3 + y^2 + z)(2y) which then comes out to 8 once you plug in everything

Now c) is where I am lost. I have no clue how to differentiate fzz :(