Hello I’m not getting this, can anyone please help me ??

Answer:
Let x = number of days
f(x) = number of algae cells
f(x) = 2,000(5^x)
The common ratio of this geometric sequence is 10,000/2,000 = 5.
2,000(5^x) = 24,000,000
5^x = 12,000
x ln 5 = ln 12,000
x = ln 12,000/ln 5 = about 5.84 days