The answer is 2 not 3/2
I suggest a recheck to it

(B) is the answer.
The formula for sun to infinity contains minusvin the denominator already i.e 1-r. Therefore when minuus is brought into the formula it becomes positive giving us 1 as the answer.

F = \(\cfrac{a}{1-r}\), \(a=?, r=?\)
To find sum to infinity, \(a\) and \(r\) are required:
\(ar = -\frac{1}{2}\)...(1)
\(ar^2 = \frac{1}{4}\)...(2)
Divide equ 2 by 1:
\(\cfrac{ar^2}{ar} = \cfrac{\frac{1}{4}}{-\frac{1}{2}}\)
\(r = -\frac{1}{2}\)
Then input the value of \(r\) in one of the equ \(a = 1\):
This gives us: \(\frac{1}{1-\frac{1}{2}} = \frac{2}{3}\)