Suppose that the amount of algae in a pond doubles every 4 hours. If the pond initially contains 50 pounds of algae, how much algae will be in the pond after 12 hours?
After 4 hours: 50 pounds x 2 = 100 pounds
After 8 hours: 100 pounds x 2 = 200 pounds
After 12 hours: 200 pounds x 2 = 400 pounds
After 12 hours, there will be 400 pounds of algae in the pond.