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: each year for 4 years , a farmer increased the number of trees in a certain orchard by 1 / 4 of the number of trees in the orchard of the preceding year . if all of the trees thrived and there were 12500 trees in the orchard at the end of 4 year period , how many trees were in the orchard at the beginning of the 4 year period . 
Options: a ) 5113 , b ) 5117 , c ) 5120 , d ) 8119 , e ) 10115
[EX A]: c

[EX Q]: Problem: find the ones digit of 73 ^ 356 
Options: a ) 1 , b ) 5 , c ) 6 , d ) 7 , e ) 9
[EX A]: a

[EX Q]: Problem: 4 , 6 , 12 , 14 , 28 , 30 , . . ? 
Options: a ) 20 , b ) 40 , c ) no = 60 , d ) 80 , e ) 100
[EX A]:
c