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: if a certain computer is capable of printing 4700 monthly credit card bills per hour , while a new model is capable of printing at a rate of 6800 per hour , the old model will take approximately how much longer than the new model to print 10000 bills ? 
Options: a ) 19 mins , b ) 29 mins , c ) 39 mins , d ) 38 mins , e ) 37 mins
c

Problem: if [ x ] is the greatest integer less than or equal to x , what is the value of [ - 2.6 ] + [ 1.4 ] + [ 2.7 ] ? 
Options: a ) 0 , b ) 1 , c ) 2 , d ) 6 , e ) 7
a

Problem: the proportion of copper and zinc in the brass is 13 : 7 . how much zinc will there be in 100 kg of brass ? 
Options: a ) 37 kg , b ) 35 kg , c ) 85 kg , d ) 45 kg , e ) 25 kg

b