Problem: four concentric circles r given . the radius of 1 st circle is x . next is 2 x , then 3 x and 4 x . given that area b / w 2 nd and 1 st is a and 4 th and 3 rd circles being b . find ratio of a to b 
Options: ['a ) 2 : 7', 'b ) 1 : 7', 'c ) 3 : 5', 'd ) 3 : 7', 'e ) 3 : 4']
d