You have to find circumference of a circle. Pi comes here because of its ratio. 2 and r comes because it equals the diameter. So pi times 2 times r is basically circumference over diameter times diameter which gives circumference.
TO simplify the answer make common denominator which would be 12 so 5/6 times 2 on each 10/12 & 3/4 x3 becomes 9/12 so those make 1 7/12 add with 1 and 7
