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: the tax on a commodity is diminished by 30 % but its consumption is increased by 15 % . find the decrease percent in the revenue derived from it ? 
Options: a ) 20 % , b ) 18 % , c ) 15 % , d ) 12 % , e ) 14 %
a

Problem: in a group of ducks and cows , the total number of legs are 8 more than twice the no . of heads . find the total no . of buffaloes . 
Options: a ) 5 , b ) 4 , c ) 6 , d ) 3 , e ) 2
b

Problem: the average weight of 5 persons increases by 1.5 kg . if a person weighing 65 kg is replaced by a new person , what could be the weight of the new person ? 
Options: a ) 76 kg , b ) 77 kg , c ) 72.5 kg , d ) data inadequate , e ) none of these

c