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: the average of the marks of 30 students in a class is 45 . if the marks of each student are doubled , find the new average ? 
Options: a ) 85 , b ) 77 , c ) 33 , d ) 90 , e ) 75
[EX A]: d

[EX Q]: Problem: a sum of money lent out at s . i . amounts to a total of $ 480 after 2 years and to $ 680 after a further period of 5 years . what was the initial sum of money that was invested ? 
Options: a ) $ 360 , b ) $ 380 , c ) $ 400 , d ) $ 420 , e ) $ 440
[EX A]: c

[EX Q]: Problem: 4 years ago , paula was 4 times as old as karl . in 12 years , paula will be twice as old as karl . what is the sum of their ages now ? 
Options: a ) 36 , b ) 40 , c ) 44 , d ) 48 , e ) 52
[EX A]:
d