This problem is about geometric sequence, which is a sequence formed by multiplying (or dividing) a constant factor.
In this case, we can observe that each new day has greater power, specifically, its exponent increases by one. This is because each day, the number of amoebas increases by a multiplying factor of 2.
Having said that, we can deduct that the fourth day is going to have a power with exponent 4, because as we said before, each day the exponent increases by 1.
So, the power of the fourth day is
[tex]2^4=16[/tex]