Problem: A farmer grows two crops, corn and soybeans. Suppose that each acre planted with corn requires 1 man day of labor, $3 investment and yields a profit of $35 at harvest. Each acre of soybeans on the other hand requires 2 man days of labor, $1 investment and returns a profit of $20 at harvest. The farmer had a total of 70 acres available for these crops. He has $140 he can invest and 80 man days of labor available. How many acres of each crop should he plant for maximum profit?