(b)
Feasible region is $OACBO$ and $\mu = 3x + 4y$
[image:12_image25.jpeg]
At point $O(0,\ 0)$
$\mu = 0 + 0 = 0$
At point $A(40,\ 0)$
$\mu = 3(40) + 4(0) = 120$
At point $B(0,\ 30)$
$\mu = 0 + 4(30) = 120$
At point $C(20,\ 20)$
$\mu = 3(20) + 4(20) = 140$
$\therefore$ The maximum value at the point $C(20,\ 20)$ is 140