Can someone me solve this? i keep getting stuck

I can't imagine why the variable in the exponent isn't 'n'.
To me, that's the only way this makes sense, and I'm
going to handle it as if the exponent is  (n - 1) .

First term:  n = 1

A(1) = -2 · 5¹⁻¹  =  -2 · 5⁰  =  -2 · 1  =  -2 .

Fourth term:  n = 4

A(4)  =  -2 · 5⁴⁻¹  =  -2 · 5³  =  -2 · 125  =  -250 .

Eighth term:  n = 8

A(8)  =  -2 · 5⁸⁻¹  =  -2 · 5⁷  =  -2 · 78,125  =   -156,250 .

The first choice on the list looks like the correct one.

The answer would be 13.5 minutes.