Answer:
first term a=4
Step-by-step explanation:
Sum of the first 6 terms S6 = 15624
common ratio r= 5
n= 6
first term a=?
Formula: S6= a(r^n-1)/r-1
15624 = a( 5^6-1)/5-1
15624 = a(15625-1)/4
15624= a( 15624)÷4
15624= 15624a÷4
Cross multiply
15624×4 = 15624a
62496 = 15624a
divide both sides by 15624
62496÷15624 = 15624a÷15624
4 = a
a= 4
