Question 972919
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PART A:
The question is unclear. We will assume X=side of square.
If 3cm=radius of coin:
{{{Area=(pi)r^2-X^2}}}
{{{Area=(pi)(9cm^2)-X^2}}}
{{{Area=9(pi)cm^2-X^2}}}
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If 3cm=diameter of coin:
{{{Area=(pi)(1.5cm)^2-X^2}}}
{{{Area=2.25(pi)cm^2-X^2}}}
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If 3cm=circumference of coin:
{{{Area=(pi)(C/2(pi))^2-X^2}}}
{{{Area=(pi)(3cm/2(pi))^2-X^2}}}
{{{Area=(pi)(9cm^2/4(pi)^2)-X^2}}}
{{{Area=9cm^2/4(pi)-X^2}}}
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PART B:
Since 3cm as radius yields the only workable solution, we will use that as example:
{{{Area=7(pi)cm^2}}}
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{{{Area=9(pi)cm^2-X^2}}}
{{{7(pi)cm^2=9(pi)cm^2-X^2}}} Subtract 7(pi)cm^2 from each side
{{{0=2(pi)cm^2-X^2}}} Add X^2 to each side.
{{{X^2=2(pi)cm^2}}} 
 Since X=side of square, area of square={{{X^2=2(pi)cm^2}}}