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 140 m long running at 84 kmph crosses a platform in 16 sec . what is the length of the platform ? 
Options: a ) 287 , b ) 298 , c ) 233 , d ) 726 , e ) 267
[EX A]: c

[EX Q]: Problem: 26 buckets of water fill a tank when the capacity of each bucket is 13.5 litres . how many buckets will be required to fill the same tank if the capacity of each bucket is 9 litres ? 
Options: a ) 30 , b ) 39 , c ) 60 , d ) data inadequate , e ) none of these
[EX A]:
b