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: 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
[A]: a

[Q]: Problem: if the product of two numbers is 45276 and their h . c . f . is 22 , find their l . c . m .
Options: a ) 2574 , b ) 2500 , c ) 2100 , d ) 2058 , e ) none of these
[A]: d

[Q]: Problem: 35 binders can bind 1400 books in 21 days . how many binders will be required to bind 1600 books in 20 days ?
Options: a ) 87 , b ) 18 , c ) 42 , d ) 16 , e ) 10
[A]:
c