## weak max principle

Hey everyone, I need a little bit of help with this question so any help would be much appreciated.

Equation: $u_y -ku_{xx}=f(x,y)$ for $0 \le x \le A$
with
$u(x,0)=g(x)$, $u(0,y)=h(y)$, $u(A,y)= j(y)$

Show the weak max principle applies to $u$ if $f \le 0$.

Any hints on how to do this question?

Thanks