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: 20 beavers , working together in a constant pace , can build a dam in 18 hours . how many hours will it take 12 beavers that work at the same pace , to build the same dam ?
Options: a ) 22 . , b ) 24 . , c ) 30 . , d ) 36 , e ) 38 .
[A]: c

[Q]: Problem: two trains of equal length , running with the speeds of 60 and 40 kmph , take 55 seconds to cross each other while they are running in the same direction . what time will they take to cross each other if they are running in opposite directions ?
Options: a ) 10 sec , b ) 16 sec , c ) 13 sec , d ) 67 sec , e ) 11 sec
[A]: e

[Q]: Problem: a man rows his boat 75 km downstream and 45 km upstream , taking 5 hours each time . find the speed of the stream ?
Options: a ) 6 kmph , b ) 5 kmph , c ) 2 kmph , d ) 3 kmph , e ) 1 kmph
[A]:
d