It is given in the question that,

Z = 3x + 4y

We have to subject on the following equation:

x ≥ 0, y ≥ 0, x + y ≤ 4

(x, y) = (0, 4), (4, 0)

We can clearly see that Z is maximum at (0, 4). Hence, maximum value of Z will be 16