Problem: twenty eight meters of wire is available to fence off a flower bed in the form of a circular sector . what must the radius of the circle in meters be , if we wish to have a flower bed with the greatest possible surface area ? 
Options: ['a ) 2 √ 2', 'b ) 2 √ 5', 'c ) 5', 'd ) 7', 'e ) none of these']
d