Matlab graphing: multivariate function with constraints

I learned a little bit of matlab graphing functions in my engineering class. In managerial accounting class I am taking right now I encountered a cost function like this:

C(q;P)=min(20z1+15z2+5z3) s.t. q1<=sqrt(z1z3), q2<=sqrt(z2z3), z3<=z3-bar=15, z1,z2,z3>0

Can anyone show me how to graph this function please? With q1,q2 being independent variables and C dependent variable.

Thanks a lot.