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: an engine moves at the speed of 60 kmph without any coaches attached to it . speed of the train reduces at the rate that varies directly as the square root of the number of coaches attached . when 4 coaches are attached speed decreases to 48 kmph . what will be the speed of train when 36 coaches are attached . 
Options: a ) 24 , b ) 28 , c ) 20 , d ) 32 , e ) 40
[EX A]: a

[EX Q]: Problem: a and b together can do a piece of work in 10 days . b alone can finish it in 20 days . in how many days can a alone finish the work ? 
Options: a ) 20 , b ) 10 , c ) 15 , d ) 5 , e ) 7
[EX A]: a

[EX Q]: Problem: the pinedale bus line travels at an average speed of 60 km / h , and has stops every 5 minutes along its route . yahya wants to go from his house to the pinedale mall , which is 8 stops away . how far away , in kilometers , is pinedale mall away from yahya ' s house ? 
Options: a ) 20 km , b ) 30 km , c ) 40 km , d ) 50 km , e ) 60 km
[EX A]:
c