Answer: 
Step-by-step explanation:
The formula for calculate the arc lenght is:

Where "r" is the radius and "
" is the central angle of the arc in degrees.
The formula used to find the circumference of a circle is:

Where "r" is the radius.
Then, we can observe that the formula for calculate the arc lenght can be rewritten in this form:

Where "C" is the circumference of the circle.
Finally we need to substitute the central angle and the circumference into
. Then the result is this:
