A retired executive has up to $8 million that he wishes to invest in apartment buildings. The following table shows the purchase price and the expected 10-year return (in millions of dollars) of the 4 buildings that he is considering.

Building 1 2 3 4 Price 4.0 3.8 6.0 7.2 Return 4.5 4.1 8.0 7.0 The executive wishes to choose investments that maximize his total return. Assume that every option is available only on an all-or-nothing basis.

(a) Formulate a knapsack ILP to choose an optimal investment plan.

(b) Solve your knapsack by inspection.