VA=vj^And VB=−vi^Time to reach from A to B=42πR×v1=2vπRDisplacement from A to B=R2Now, Average velocity from A to B=TimeDisplacement=2vπRR2=π22vInstantaneous velocity at B is −vi^According to question, average velocity instantaneous velocity =x2ππ22vv=x2π⇒22π=x2π⇒x=2