If the diameter is 12, then the radius is 6.  If you know that D is a point on the big circle and that B is the center, then you know that BD has a measurement of 6.  BD isalso the diameter of the smaller circle, so the radius is 6 / 2 = 3.  The area of a circle is
Pr²:
 3²P  = 9P  (B)
 
 
 

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