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'.

Problem: ( 18 ) 7 x ( 5832 ) - 2 ÷ ( 324 ) - 1 = ( 18 ) 7 
Options: a ) 5 , b ) 4 , c ) 3 , d ) 2 , e ) 1
c

Problem: solution x is 10 percent alcohol by volume , and solution y is 30 percent alcohol by volume . how many milliliters of solution y must be added to 150 milliliters of solution x to create a solution that is 25 percent alcohol by volume ? 
Options: a ) 250 / 3 , b ) 500 / 3 , c ) 400 , d ) 450 , e ) 600
d

Problem: the units digit of ( 35 ) ^ ( 87 ) + ( 93 ) ^ ( 47 ) is : 
Options: a ) 2 , b ) 4 , c ) 6 , d ) 8 , e ) 0

a