Since \(y\) has a negative coefficient in \(Z\), we want the smallest \(y\) (take \(y=0\)) and the largest \(x\) allowed.
With \(y=0\), the constraint becomes \(x\le13\).
Corner checks:
\((13,0)\Rightarrow Z=13\) (best), \((0,13)\Rightarrow Z=-39\), \((0,0)\Rightarrow Z=0\).