Z = 18x + 9y
The maximum or minimum value occurs at corner points.
Let A(2, 72), B(15, 20), C(40, 15)
${\mathit{Z}}_{\mathit{A}}=18\times 2+9\times 72=684$
${\mathit{Z}}_{\mathit{B}}=18\times 15+9\times 20=450$
${\mathit{Z}}_{\mathit{C}}=18\times 40+9\times 15=855$
Maximum occurs at point C(40,15) and minimum occurs at point B(15,20)