What is the arc length of the the arc subtended in a circle with radius 6 and an angle of 7pi/8

First, find the fraction of the circumference represented by central angle 7pi/8:

 7pi/8
 
   2pi

Then find the circumference; it is C = 2 pi r, or 2pi(6), or 12 pi units

Then the arc length is   7pi/8                  7
                                      * 12 pi = units, or 21/4 units, or 5 1/4 units. 
                                       2pi                   16 pi

The answer simplified would be. -6300x