Radius times radians equals arc length

A circle with the following information:

Arc length: 9 cm and radius: 4 cm 

Circumference of the circle = 8 pi

The central angle:

2 pi (9/(8 pi)) 

= 2.25 radians = 128.9° (degrees)

Are you looking for the angle  , @ ?

then you have the answer...   S = r@,  S = 9 cm    r = 4 cm

@ = S / r   =  9 / 4 = 2.25 radians 

you only can use/ get radians in the arc length formula  S = r@ ...if  degrees  are wanted, you need to mult 2.25 rad  by [ 180˚ / (π radians) ]  to convert  the answer to degrees...