Question 191225
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The shaded area you're referring I guess is the Area outside the inner circle.


We'll see the figure:
{{{drawing(400,400,-6,6,-6,6,circle(0,0,2.5),circle(0,0,4.5),green(circle(0,0,2.6)),green(circle(0,0,2.7)),green(circle(0,0,2.8)),green(circle(0,0,2.9)),green(circle(0,0,3)),green(circle(0,0,3.1)),green(circle(0,0,3.2)),green(circle(0,0,3.3)),green(circle(0,0,3.4)),green(circle(0,0,3.5)),green(circle(0,0,3.6)),green(circle(0,0,3.7)),green(circle(0,0,3.8)),green(circle(0,0,3.9)),green(circle(0,0,4)),green(circle(0,0,4.1)),green(circle(0,0,4.2)),green(circle(0,0,4.3)),green(circle(0,0,4.4)),arrow(0,0,-2.5,0),arrow(0,0,4.5,0),red(circle(0,0,.08)),red(locate(-2,1,r[i]=20ft)),red(locate(1.7,1,r[o]=36ft)),red(locate(0,3.6,Area[shaded])))}}}



Then, working Eqn ----> {{{A=pi*r^2}}}


First, find the Area of Inner circle.
{{{A[i]=pi*r[i]^2=pi*20^2}}}
{{{red(A[i]=400*pi)}}}sq.ft.



Next, find the Area of Outer Circle.
{{{A[o]=pi*r[o]^2=pi*36^2}}}
{{{red(A[o]=1296*pi)}}}sq.ft.



So, {{{Area[sh]=A[o]-A[i]=1296*pi-400*pi}}}
{{{red(highlight(A[sh]=896*pi))}}}sq.ft. (Answer)



Thank you,
Jojo</font>