Question

CAN Someone help me

Answer 1

by definition of radians we have \(\large S=r\theta\) where S is the arc length
in your question x=S

Answer 2

The arc with length x is to the entire circumference (2*pi*r) of the circle as the central angle 78 is to the entire circle in degrees, 360.

That means the following:
78/360 = x / (2*pi*3)

13 / 60 = x / (6*pi) --> Solve for x.

@LynettaSB