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: if xy > 0 , 1 / x + 1 / y = 4 , and 1 / xy = 6 , then ( x + y ) / 2 = ? 
Options: a ) 1 / 25 , b ) 1 / 6 , c ) 1 / 5 , d ) 1 / 3 , e ) 6
[A]: d


[Q]: Problem: 48.95 - 32.006 = ? 
Options: a ) 16.089 , b ) 16.35 , c ) 16.89 , d ) 16.944 , e ) none of them
[A]: d


[Q]: Problem: in cliff ’ s impressive rock collection , there are half as many igneous rocks as sedimentary rocks . of the igneous rocks , 1 / 3 are shiny and the rest are matte , while 1 / 5 of the sedimentary rocks are shiny . if there are 30 shiny igneous rocks , how many total rocks does cliff have ? 
Options: a ) 30 , b ) 45 , c ) 270 , d ) 90 , e ) 135
[A]:
c