The formula for arc length is:

s is the arc length
r is the radius
theta will be in radians
In this case:
s = unknown
r = 8 cm
theta =

^^^Plug this into formula given above

Cross multiply
s * 1 =
* 8
s =

s =

^^^This is your arc length
Hope this helped!
~Just a girl in love with Shawn Mendes