To solve the problem you use an exponential equation. Since there are 90 pounds of algae to begin with, we know that a=90. The amount is being doubled to 2 is the common ration, b. So, so far the function is f(x)=90*2^x. Now we just need to plug in x. The interval is every 4 hours so we divide 12 by 4. So now to solve the function f(x)=90*2^3. 2 cubed is 8. 8 * 90 is 720 so the answer is 720 pounds of algae after 12 hours
