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: pipes a and b can fill a tank in 3 and 4 hours . pipe c can empty it in 4 hours . if all pipes are opened together , then the tank will be filled in ? 
Options: a ) 3 hr , b ) 1 / 2 hr , c ) 1 hr , d ) 9 / 7 hr , e ) 5 / 3 hr
[EX A]: a

[EX Q]: Problem: calculate the speed of a boat in still water ( in km / hr ) if in one hour , the boat goes 10 km / hr downstream and 4 km / hr upstream . 
Options: a ) 7 kmph , b ) 8 kmph , c ) 9 kmph , d ) 7 kmph , e ) 6 kmph
[EX A]: a

[EX Q]: Problem: a train 120 m long is running at 60 kmph . in how much time will it pass a platform 240 m long ? 
Options: a ) 15.6 seconds , b ) 24.6 seconds , c ) 21.6 seconds , d ) 30.6 seconds , e ) 35.6 seconds
[EX A]:
c