i don't understand what you're quastion is
so let me tell you something
if you see when we go up from 1 its start to twice the number
for example
f(n)=2f(n-1)
let n equal to 2
f(2)=2f(1)
and f(1)=3
so f(2)=6
lets continue
let n equal to 3
f(3)=2f(2)
and f(2) equal to 6
so f(3)=12
so we relaised that when we go up from 1 its start to twice
and we take down number from 1 its start to take half
for example
f(n)= 2f(n-1)
let the n equal to 1
f(1)=2f(0)
f(1)=3 so
3=2f(0)
f(0)=3/2
now let the n equal to 0
f(0)=2f(-1)
f(0)=3/2
f(-1)=3/4
so we can make this equation
f(x)=3/2×(2)^x
we can sample it
so its become
f(x)=3×(2)^(x-1)
have a great day and Sorry for my bad engilish i try my best to explain
