F(n)=5xf(n-1)
f(0)=5
f(3)=
(x means multiple)

625

Explanation:

So this says the following:

A term is equal to 5 times the previous term.

We are given the 0th- term is 5.

The first term is 5(5)=25.

The second term would be 5(25)=125.

The third term would be 5(125)=625.

So f(3)=625.

If you didn't like that explanation, you can find f(3), by first finding f(1) then f(2) using the equation given as is without making the interpretation I did above.

; plug in 1 for :

; plug in 2 for :

; plug in 3 for :

Explanation:

All results are quintupled the previous terms:

I am joyous to assist you anytime.