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 man can do a piece of work in 4 days , but with the help of his son he can do it in 3 days . in what time can the son do it alone ? 
Options: a ) 12 days , b ) 6 days , c ) 5 days , d ) 4 days , e ) none of these
a

Problem: a 21 cm long wire is to be cut into two pieces so that one piece will be 2 / 5 th of the other , how many centimeters will the shorter piece be ? 
Options: a ) 12 , b ) 6 , c ) 88 , d ) 77 , e ) 14
b

Problem: a hollow spherical metallic ball has an external diameter 6 cm and is 1 / 2 cm thick . the volume of metal used in the metal is : 
Options: ['a ) 47 1 / 5 cm 3', 'b ) 47 3 / 5 cm 3', 'c ) 47 7 / 5 cm 3', 'd ) 47 9 / 5 cm 3', 'e ) none of these']

b