Consider the following linear programming problem:
Max Z = $15x + $20y
Subject to: 8x + 5y ≤ 40
0.4x + y ≥ 4
x, y ≥ 0
Considering that the values for x and y that will maximize revenue are respectively x = 0 and y = 8, what is the amount of surplus associated with the second constraint – in the optimal point?