A company contracts to paint 3 houses. Mr.Brown can paint a house in 6 days while Mr.Black would take 8 days and Mr.Blue 12 days. After 8 days Mr.Brown goes on vacation and Mr. Black begins to work for a period of 6 days. How many days will it take Mr.Blue to complete the contract?

 A company contracts to paint 3 houses. Mr.Brown paints in 6 days = 1 house Mr.Brown paints in 1days =1/6 house Mr.Brown paints in 8days =8/6 =4/3 house work left = 3-4/3 = 5/3 house Mr.Black paints in 8 days = 1 house Mr..Black paints in 1days =1/8 house Mr..Black paints in 6days =6/8= 3/4 house work left = 5/3 - 3/4 = 11/12= .Blue paints in 12 days = 1 house .Blue paints in 1 day = 1/12 house Mr. blue will finish 11/12 huse in = (11/12)/12=11 days