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'.

[Q]: Problem: a and b together do a work in 20 days . b and c together in 15 days and c and a in 12 days . so a , b and c together finish same work in how many days ? 
Options: a ) 12 , b ) 15 , c ) 8 , d ) 10 , e ) 11
[A]: d


[Q]: Problem: the speed at which a man can row a boat in still water is 15 km / hr . if he rows downstream , where the speed of current is 3 km / hr , how many seconds will he take to cover 90 meters ? 
Options: a ) 12 , b ) 16 , c ) 17 , d ) 18 , e ) 20
[A]: d


[Q]: Problem: a can do a piece of work in 6 days and b can do it in 6 days how long will they both work together to complete the work ? 
Options: a ) 6 / 11 , b ) 1 / 2 , c ) 3 / 4 , d ) 9 / 11 , e ) 10 / 11
[A]:
b