soppose that the amount of algae ina pond doubles every 4 hours. if the pond initially contains 90 pounds of algae, how much algae will be in the pond after 12 hours?

If the amount of algae in the pond doubles every 4 hours, then after 4 hours there will be 90*2 = <<90*2=180>>180 pounds of algae in the pond.

After the next 4 hours, the amount of algae will double again to 180*2 = <<180*2=360>>360 pounds.
Finally, after another 4 hours, the amount of algae will double again to 360*2 = <<360*2=720>>720 pounds.
Therefore, after 12 hours, there will be 720 pounds of algae in the pond. Answer: \boxed{720}.