Answer: C
Step-by-step explanation:
S = [tex]\frac{a}{1-r}[/tex]
a = 80, r = [tex]-\frac{1}{4}[/tex]
S = [tex]\frac{80}{1-(-\frac{1}{4})}[/tex]
= [tex]\frac{80}{\frac{5}{4}}[/tex]
= [tex]\frac{80*4}{5}[/tex]
= 64
