Question

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Answer 1

area of the ring = π (42² - 21²) = 4158 cm²

now, we have to remove some parts,

that part = (sector formed by bigger circle) -( sector formed by smaller circle)

=π (42)²×60°/360 -π(21)² ×60°/360°

=(π/6)×(42² -21²) = 693 cm²

so the required area = 4158 - 693 = 3465 cm²