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'.

[EX Q]: Problem: in a river flowing at 2 km / hr , a boat travels 40 km upstream and then returns downstream to the starting point . if its speed in still water be 6 km / hr , find the total journey time . 
Options: a ) 10 hours , b ) 12 hours , c ) 14 hours , d ) 15 hours , e ) none of these
[EX A]: d

[EX Q]: Problem: 49 ã — 49 ã — 49 ã — 49 x 49 = 7 ? 
Options: a ) 4 , b ) 7 , c ) 8 , d ) 10 , e ) none of these
[EX A]: d

[EX Q]: Problem: a number is doubled and 9 is added . if resultant is trebled , it becomes 51 . what is that number 
Options: a ) 4 , b ) 10 , c ) 12 , d ) 14 , e ) 15
[EX A]:
a