Answer:
The graph in the attached figure
Explanation:
we have
This is a exponential function of the form

where
a is the initial value
b is the base
In this problem
a=20 g
b=2
Remember that
b=1+r
so
1+r=2
r=2-1=1
r=100% (the amount of algae in a fish tank doubles every day)
using a graphing tool
The graph in the attached figure