Problem: if a drawing has an outer circle of diameter 30 and an inner circle of diameter 24 , then what fraction of outer circle ' s surface is not covered by the inner circle ? 
Options: ['a ) 3 / 6', 'b ) 8 / 24', 'c ) 14 / 16', 'd ) 9 / 25', 'e ) 2 / 3']
d