You are in charge of buying office supplies for your business. Your workers use red and black pens. Red pens cost $5 per box and black pens cost $3 per box. You need at least 10 boxes of pens. You want no more than 7 boxes of black pens and no more than 6 boxes of red pens. You want to minimize the cost to your business.

The objective function for this situation is C = 5x + 3y. What (x, y) pair minimizes cost?
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(6, 7)

(0, 7)

(3, 7)

(6, 4)