Please see attached picture.

Answer:
B
Step-by-step explanation:
the arc length is calculated as
arc = circumference of circle × fraction of circle
= 2πr × [tex]\frac{90}{360}[/tex]
= 2π × 16 × [tex]\frac{1}{4}[/tex]
= 32π × [tex]\frac{1}{4}[/tex]
= [tex]\frac{32\pi }{4}[/tex]
= 8π ft