Answer:
2.96cm
Step-by-step explanation:
C= 2x Pi x Radius
9.31 = 2 x Pi x Radius
9.31/2 = Pi x Radius
4.655 = Pi x Radius
4.655/3.14 = Radius
1.4824840764331210191082802547771 = Radius
Now, that you have worked out the radius which is half the diameter
Radius + Radius = Diameter
1.4824840764331210191082802547771 + 1.4824840764331210191082802547771 = 2.964968153
= 2.96cm to 2 d.p
You can double check because C= 2 x Pi x Radius
9.31 = 2 x 3.14 x 1.482