At the price of $5 per pack of batteries, Duracell sells 10,000 packs of batteries and Energizer sells 15,000 packs of batteries. When the price rises to $7.50, Duracell sells 12,000 packs of batteries and Energizer sells 16,000 packs of batteries. What is the market supply at $7.50? Choose one: A. 16,000 B. 25,000 C. 4,000 D. 12,000 E. 28,000