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: a and b together can do a piece of work in 6 days and a alone can do it in 13 days . in how many days can b alone can do it ? 
Options: a ) 12 days , b ) 15 days , c ) 78 / 7 days , d ) 21 days , e ) 22 / 7 days
[EX A]: c

[EX Q]: Problem: a train 110 meters long completely crosses a 280 meters long bridge in 38 seconds . what is the speed of the train is ? 
Options: a ) 32 , b ) 45 , c ) 40 , d ) 66 , e ) 09
[EX A]: c

[EX Q]: Problem: machine a can finish a job in 4 hours , machine в can finish the job in 2 hours , and machine с can finish the job in 6 hours . how many hours will it take for a , b , and с together to finish the job ? 
Options: a ) 4 / 3 , b ) 6 / 5 , c ) 8 / 7 , d ) 10 / 9 , e ) 12 / 11
[EX A]:
e