In this task, you need to answer the given multiple-choice question on the physics. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

[EX Q]: Problem: twelve machines , each working at the same constant rate , together can complete a certain job in 6 days . how many additional machines , each working at the same constant rate , will be needed to complete the job in 3 days ? 
Options: a ) 14 , b ) 12 , c ) 15 , d ) 16 , e ) 18
[EX A]: b

[EX Q]: Problem: a hall 36 m long and 15 m broad is to be paved with stones , each measuring 8 dm by 5 dm . the number of stones required is : 
Options: a ) 180 , b ) 1800 , c ) 18 , d ) 18000 , e ) 1350
[EX A]: e

[EX Q]: Problem: steve traveled the first 2 hours of his journey at 40 mph and the last 3 hours of his journey at 80 mph . what is his average speed of travel for the entire journey ? 
Options: a ) 60 mph , b ) 56.67 mph , c ) 53.33 mph , d ) 64 mph , e ) 66.67 mph
[EX A]:
d