Utilization of a Constraint

Flying High only has so much space on the plane for seating. The airline can charge $900 for a first class ticket while it can only charge $300 for an economy ticket. The contribution margin on each are $600 and $150 respectively. The big difference is that a first class seat takes up 30 square feet while an economy seat only takes up 12 square feet. If the airline has only 1,650 square feet for seating and a demand of 35 first class tickets and 90 economy seats, how many of each type of seat should they design in the plane?