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'.

Problem: a hollow iron pipe is 21 cm long and its external diameter is 8 cm . if the thickness of the pipe is 1 cm and iron weights 8 g / cm cube , then find the weight of the pipe . 
Options: ['a ) 3.696 kg', 'b ) 3.686 kg', 'c ) 2.696 kg', 'd ) 2.686 kg', 'e ) none of these']
a

Problem: a tank with a volume of 20 cubic feet has one inlet pipe and 2 outlet pipes . the inlet pipe fills water into the tank at the rate of 5 cubic inches / min and the 2 outlet pipes empty it out at the rates of 9 cubic inches / min and 8 cubic inches / min respectively . if all 3 pipes are opened when the tank is full , how many minutes does it take to empty the tank ? ( 1 foot = 12 inches ) 
Options: a ) 2110 , b ) 2220 , c ) 2440 , d ) 2660 , e ) 2880
e

Problem: a group of men decided to do a work in 8 days , but 3 of them became absent . if the rest of the group did the work in 10 days , find the original number of men ? 
Options: a ) 15 , b ) 20 , c ) 30 , d ) 25 , e ) 18

a