Problem: two circular frames are kept one above the other . frame x has a diameter of 16 cm and frame y has a diameter of 12 cm . what fraction of the surface of frame x is not covered by frame y ? 
Options: ['a ) 3 / 5', 'b ) 7 / 16', 'c ) 12 / 16', 'd ) 24 / 12', 'e ) 2 / 3']
b