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: x can finish a work in 25 days . y can finish the same work in 20 days . y worked for 12 days and left the job . how many days does x alone need to finish the remaining work ? 
Options: a ) 2 , b ) 5 , c ) 6 , d ) 7 , e ) 8
e

Problem: r is the set of positive even integers less than 20 , and s is the set of the squares of the integers in r . how many elements does the intersection of r and s contain ? 
Options: ['a ) none', 'b ) two', 'c ) three', 'd ) five', 'e ) seven']
c

Problem: r is the set of positive odd integers less than 50 , and s is the set of the squares of the integers in r . how many elements does the intersection of r and s contain ? 
Options: a ) none , b ) two , c ) four , d ) five , e ) seven

c