If you buy ' N ' of each item, then you'll pay 3.99N for brushes,
21.79N for cans of paint, and 6.89N for rollers.
The question assures us that you bought the same number of
each item. So your total bill at the hardware store checkout is
3.99N + 21.79N + 6.89N
= N (3.99 + 21.79 + 6.89)
= 32.67 N .