4/5which expression could be modeled using the diagram 4/5

The explicit formula for the sum of the geometric series is:
Sn=[a(rⁿ-1)]/(r-1)
where:
a=first term
n=number of terms
r=common ratio
From the series given:
5 + 25 + 125 + 625 + 3,125 + 15,625?
a=5
r=5
n=6
thus the sum of the series will be:
Sn=[5(5⁶-1)]/(5-1)
Sn=(5(15625-1))/4
Sn=78120/4
Sn=19530

19530