The feasible region is the triangle with vertices where the lines meet:
\((0,0)\), \((25,0)\), \((0,25)\). A linear objective hits its max at a vertex.
Evaluate \(Z\):
\((25,0)\Rightarrow Z=6\cdot25+3\cdot0=150\).
\((0,25)\Rightarrow Z=0+75=75\).
\((0,0)\Rightarrow Z=0\).
So the maximum is \(150\) at \((25,0)\).