A housing contractor has subdivided a farm into 100 building lots. She has designed two types of homes for these lots: colonial and ranch style. A colonial requires $30,000 of capital and produces a profit of $4000 when sold. A ranch style house requires $40,000 of capital and provides an $8000 profit. If the contractor has $3.6 million of capital on hand, how many houses of each type should she build for maximum profit? Will any of the lots be vacant?