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: three pipes , a , b , & c are attached to a tank . a & b can fill it in 20 & 30 minutes respectively while c can empty it in 15 minutes . if a , b & c are kept open successively for 4 minute each , how soon will the tank be filled ?
Options: a ) 2 hours , b ) 12 hours , c ) 3 hours , d ) 5 hours , e ) 6 hours
[A]: b

[Q]: Problem: a 600 meter long train crosses a signal post in 15 seconds . how long will it take to cross a 3 kilometer long bridge , at the same speed ?
Options: a ) 4 min , b ) 2 min , c ) 8 min , d ) 9 min , e ) 1.5 min
[A]: e

[Q]: Problem: 16 boys or 24 girls can construct the wall in 6 days . the number of days that 4 boys and 12 girls will take to construct ?
Options: a ) 7 days , b ) 14 days , c ) 6 days , d ) 8 days , e ) 9 days
[A]:
d