Question 1107007
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The area of the outer ring is the difference 

    A = {{{pi*(3a)^2}}} - {{{pi*(2a)^2}}} = {{{pi*(9a^2 - 4a^2)}}} = {{{5pi*a^2}}}.



The area of the middle ring is the difference 

    A = {{{pi*(2a)^2}}} - {{{pi*a^2}}} = {{{pi*(4a^2 - a^2)}}} = {{{3pi*a^2}}}.
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