Answer:
4
Step-by-step explanation:
The sum of n terms of a geometric series with first term a1 and common ratio r is given by ...
Sn = a1·(r^n -1)/(r -1)
for r=5 and n=6, this becomes ...
15624 = a1·(5^6 -1)/(5 -1) = a1·(15624/4)
Then we have ...
1 = a1/4 . . . . . divide by 15624
4 = a1 . . . . . . multiply by 4
The first term of the series is 4.
