Okey, in this case we need to find first all the play of circumference of the circle:
2πr
2*3.5*22/7
Total: 22 inches
Considering that the circle is divided into 5 equal parts, we will divide thw total by five:
22/5= 4.4 inches
The distance between all parts of the circle is 4.4 inches, so the distance between a and b is 4.4 inches.