Answer:
720 pounds
Step-by-step explanation:
Initially, we have that the amount of algae in the pond is [tex]90pounds[/tex]. Every four hours the amount of algae doubles. If we called [tex]t[/tex] the time and [tex]W[/tex] the amount of algae, we have that:
[tex]At \ t=0 \ hours, \ w=90 \ pounds \\ \\ At \ t=4 \ hours, \ w=2(90)=180 \ pounds \\ \\ At \ t=8 \ hours, \ w=2(180)=360\ pounds \\ \\ At \ t=12 \ hours, \ w=2(360)=720 \ pounds[/tex]
Finally, after 12 hours the amount of algae in the pond is 720 pounds
