Example 3: A farmer has 8 acres of land and can plant wheat or barley. The farmer earns $5000 for each acre of wheat and $3000 for each acre of barley. To grow successfully, wheat requires
2 gallons of pesticide per acre and barley requires 1 gallon of pesticide per acre. However, laws
restrict the farmer to using no more than 10 gallons of pesticide for his entire farm. How many
acres of wheat and barley should the farmer grow to make the most money?