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The correct answer is 1,440 pounds.
After 4 hours, the amount of algae in the pond will be 90 x 2 = 180 pounds.
After 8 hours, the amount of algae in the pond will be 180 x 2 = 360 pounds.
After 12 hours, the amount of algae in the pond will be 360 x 2 = 720 pounds.