The area of the ring with radii 10 and 20 equal to -942.45
A ring is a flat geometric shape bounded by two concentric circles.
Ring area formula 
where R is the radius of the outer circle, r is the radius of the inner circle.
where D is the diameter of the outer circle, d is the diameter of the inner circle.Solution:
S = π·(R2-r2)
= π·(102-202)
= π·(100-400)
= -300π
=
-942.45
a: The area of the ring with radii 10 and 20 equal to -942.45