Problem: a circular mat with radius 10 inches is placed on a square tabletop , each of whose sides is 24 inches long . which of the following is closest to the fraction of the tabletop covered by the mat ? 
Options: ['a ) 5 / 12', 'b ) 2 / 5', 'c ) 0.5451', 'd ) 3 / 4', 'e ) 5 / 6']
c