How do you solve step by step the answers are 1000 and 4000

The correct answer is shown. Product DGH has a monthly demand of 5,000 units. Its contribution margin is $18 per unit and $36 per direct labor hour. Product RBG has a monthly demand of 4,000 units. It's contribution margin is $15 per unit and $60 per direct labor hour. If the company only has 1,500 direct labor hours available, the company should produce 1,000 units of Product DGH and 4,000 units of Product RBG. (Enter your answers as whole numbers.)