In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Problem: if a - b = 5 and a 2 + b 2 = 31 , find the value of ab . 
Options: a ) 9 , b ) 2 , c ) 3 , d ) 7 , e ) 12
c

Problem: a number is doubled and 5 is added . if the resultant is trebled , it becomes 123 . what is that number ? 
Options: a ) 12 , b ) 29 , c ) 27 , d ) 18 , e ) 99
d

Problem: 60 % of x is greater than 1 / 3 rd of x by 110 . what is x ? 
Options: a ) 100.5 , b ) 200.5 , c ) 300.5 , d ) 350.5 , e ) 412.5

e