Range = max-min= 150-119 = 31
I think you count the squares in the middle or radius ?
Ok so we know that the distance around the circle (or circumference) is equal to the diameter times pi.
This means that

d being the diameter,
This means that:

= 12.00028271
= 12 m
So the diameter of the circle is 12 metres.
Hope this helped
Area of circle = πd²/4, where d = diameter
= π*6*6/4 = 9π ≈ 9 *3.1416 ≈ 28.2744 cm²
Area ≈ 28.27 cm²
Hope this explains it.