How to calculate the circumference of a circle.
The circumference of a circle can be calculated using the formula:
2 x π x r
Where π (pi) = approx 3.14
and...

How to find the area of an annulus
The area = π x (Outer Radius 2 - Inner radius 2)
Example:
π = 3.14
Outer Radius = 10 cm
Inner radius = 8 cm
Area =...