A farmer plants white rice and brown rice on 10 acres of land. He must use pesticide on all 10 acres and he has 18 liters of pesticide to use. White rice requires 2 liters of pesticide per acre and brown rice requires 1 liter of pesticide per acre. If he can earn $5000 for each acre of white rice and $3000 for each acre of brown rice, how many acres of each should he plant to maximize his earnings? What are his maximum earnings?