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: village x has a population of 72000 , which is decreasing at the rate of 1200 per year . village y has a population of 42000 , which is increasing at the rate of 800 per year . in how many years will the population of the two villages be equal ? 
Options: a ) 15 , b ) 19 , c ) 11 , d ) 18 , e ) 13
[A]: a


[Q]: Problem: if ( a - b - c + d = 13 ) and ( a + b - c - d = 9 ) , what is the value of ( b - d ) ^ 2 ? 
Options: a ) 4 . , b ) 8 . , c ) 12 . , d ) 16 . , e ) 64 .
[A]: a


[Q]: Problem: the sum of the squares of three numbers is 138 , while the sum of their products take two at a time is 131 . find the sum ? 
Options: a ) 10 , b ) 30 , c ) 20 , d ) 50 , e ) 40
[A]:
c