Non Linear Equations without the Matrix

[lksgman]

Hello to anyone, first of all I am new in this forum and I recently got my HP Prime. I am using it to study functions with many variables. Right now I am with the topic of Max and Minimum values with restrictions. So after making the derivatives. I get stuck because I do not know how to find the values that will make those values 0 . So please anybody knows how to use the calculator in those aspects.

Example:
F(x,y,z,λ)= xyz-λ(2x+3y+4z-90)

Derivatives
Fx=yz-2λ=0
Fy=xz-3λ=0
Fz=xy-4λ=0
Fλ=-2x-3y-4z-90=0

So I need to find the Xs,Ys,Zs and λs that make those values 0. So that would be it and any help I will appreciate it.