Geometric series: Finite and infinite

Question

n=5
a1=243
r=2/3
i=1
This is the equation
243(2/3)^i
My answer is 633

n=infinity sign
a1=5
r=-1/4
i=1
The equation
5(-1/4)^i-1
I think its undefined

Answer 1

a1=243
r = 2/3
an = 243(2/3)^(n-1)
a5 = 48

s = a/(1-r) = 5/(5/4) = 4