A circle has a radius of 20 cm and a central angle that measures 216° find the length of the arc defined by the central angle

Can someone explain to me how to do this problem ?

Astudent is performing an experiment comparing sound and light waves. the student gathers the following data. what conclusion does the student most likely make based on this data? light waves always travel the same speed; however, the speed of sound is determined by the medium that it travels through. all sound waves always have the same energy, so the temperature of the medium does not affect wave speed. light needs to vibrate particles, so it travels fastest in tightly packed solids, while sound does not need a medium, so it travels fastest in a gas. tightly packed particles in solids slow down the light waves; however, sound waves make particles bounce into each other, so they travel faster in solids.

When a spring is compressed, the energy changes from kinetic to potential. which best describes what is causing this change? work power gravitational energy chemical energy