An airplane company is determining the difference in selling price if rows of first-class seats are added to a new design. Using the average selling price of $1,000 per first-class seat, the total selling price for one new row is f(r) = 4,000r. Each row in first class eliminates two rows of economy seats. Using the average selling price of $150 per economy seat, the total price for each pair of removed rows is e(r) = 1,800r.
The change in selling price is the value of the added first-class seats minus the value lost from removing economy seats. Subtract the functions: d(r) = f(r) − e(r) = 4,000r − 1,800r = 2,200r. Therefore, the change is d(r) = 2,200r, choice A.
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