Min and max of the function f(x,y) =3x-y

Question

Having some troubles supposed to find the minimum and maximum to this but since I've been gone I missed the work and got behind

Answer 1

To find the minimum and the maximum you have to locate first the critical points of f(x,y). But since f_{x}(x,y)=3 and f_{y}(x,y)=-1 the function f has no critical points. Actually the function f is not bounded and so there is no global min or global max and since there are no critical points there are no local min and local max.