help me please! i’m unsure of the formula and how to solve

Answer:
12.4 cm
Step-by-step explanation:
arc AB is calculated using
arc = circumference × fraction of circle
= 2πr × [tex]\frac{90}{360}[/tex]
= 2π × 7.9 × [tex]\frac{1}{4}[/tex]
= [tex]\frac{7.9\pi }{2}[/tex] ≈ 12.4 cm ( to the nearest tenth )