A farmer in Nebraska owns 1000 acres of land. He is going to plant each acre with either corn or soybeans. Let x denote the number of acres planted with corn and y denote the number of acres planted with soybeans. Each acre planted with corn requires 4 workers and 3 tons of fertilizer. Each acre planted with soybeans requires 5 workers and 4 tons of fertilizer. The farmer has 1000 workers and 1200 tons of fertilizer available. Which of the following describe the farmer's constraint(s)?