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'.

[Q]: Problem: jacob is 39 years old . he is 3 times as old as his brother . how old will jacob be when he is twice as old ? 
Options: a ) 63 , b ) 64 , c ) 65 , d ) 76 , e ) 67
[A]: c


[Q]: Problem: x varies inversely as square of y . given that y = 3 for x = 1 . the value of x for y = 5 will be equal to : 
Options: a ) 3 , b ) 6 , c ) 1 / 9 , d ) 1 / 3 , e ) 9 / 25
[A]: e


[Q]: Problem: a mixture contains milk and water in the ratio 5 : 4 . on adding 30 litters of water , the ratio of milk to water becomes 5 : 7 . total quantity of milk & water before adding water to it ? 
Options: a ) 90 , b ) 120 , c ) 80 , d ) 70 , e ) 60
[A]:
a