Answer:
4
Step-by-step explanation:
The sum to n terms of a geometric sequence is
[tex]S_{n}[/tex] = [tex]\frac{a(r^n-1)}{r-1}[/tex]
where a is the first term and r the common ratio
Here r = 5 and a has to be found, thus
[tex]S_{6}[/tex] = [tex]\frac{a(5^6-1)}{5-1}[/tex], so
[tex]\frac{a(15625-1)}{4}[/tex] = 15624
Multiply both sides by 4
15624a = 62496 ( divide both sides by 15624
a = 4
