A & B can do work in 12 days while B & C do it in 6 days. after A had worked on it for 3 days & B for 4 days.C finished the work in 7 days. in how munch days could each do th work separately?

• Let a,b,c be the number of days in which A,B and C complete the work alone respectively.
  
  after A had worked on it for 3 days & B for 4 days.C finished the work in 7 days.
  4*(1/b+1/c)+3*(1/a+1/c)=1
  4*1/6 + 3*(1/a+1/c)=1
  3*(1/a+1/c)=1/3
  (1/a+1/c)=1/9
  1/a +1/b =1/12
  1/b + 1/c = 1/6
  
  solving these, we get
  a=72, b= 72/5 days, c= 72/7 days
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