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: if n is an integer , f ( n ) = f ( n - 1 ) - n and f ( 4 ) = 14 . what is the value of f ( 6 ) ? 
Options: a ) 3 , b ) 0 , c ) 1 , d ) 2 , e ) 4
[EX A]: a

[EX Q]: Problem: patrick purchased 60 pencils and sold them at a loss equal to the selling price of 20 pencils . the cost of 60 pencils is how many times the selling price of 60 pencils ? 
Options: a ) 0.75 , b ) 0.8 , c ) 1 , d ) 1.33 , e ) 1.75
[EX A]: d

[EX Q]: Problem: the units digit of ( 10 ) ^ ( 87 ) + ( 93 ) ^ ( 46 ) is : 
Options: a ) 9 , b ) 4 , c ) 6 , d ) 8 , e ) 0
[EX A]:
a