It would be A
Each step it is multiplied by 5 to get the next step
So,
Common ratio: r=5
Explicit: a= -4 • 5^(n-1)
This simply means it starts at -4 and will increase by a multiple of 5 for every n.
Also you must say 5^(n-1) so when starting at n=1 in your sequence the formula will by a=-4• 5^(1-1) or -4•5^(0) or -4•1 so a=-4
Then, the 8th term (n=8) would be a(8) = -4•5^(8-1) or -4•5^(7) or -4•78,125 so a(8)=-312,500