It is given in the question that the end of a pendulum with a length of 21 cm travels an arc length of 24 cm.
So here radius is 21 cm and the arc length is 24 cm .
Now we use the arc length formula , which is

Where s is the arc length and r is the radius.
Substituting these values, we will get

And now we need to convert radian to degree, and for that we have to multiply by

That is
