Answer:
C = pi * d = 2 * pi *r
Step-by-step explanation:
The circumference of a circle is the distance around the circle.  It can be found by multiplying the diameter times pi.
C = pi * d
We can replace the diameter with twice the radius
C = pi * 2 * r = 2 * pi *r
 
        
             
        
        
        
Step by step:
GR-8 = 34x - 12
• move variable to left hand side
-34x + gr -8 = - 12
• change expression and move to right side
-34x = - 12 - gr - 8
• calculate sum 
-34x = - 4 - gr
• divide both sides 
X = 2/17 + 1/34gr
And there’s your answer :)