Question 44856
I have created a spreadsheet with Microsoft excel to find the number, since I could not think of a method which would not be extremely tedious without the use of a computer program. 
If we call the number of the house x, from the statements you have been given we can deduce:
(x+1)/8 is an integer (i.e. a whole number)
(x+5)/9 is an integer
(x+2)/11 is an integer
The computer program I created checks these statements and then highlights one result: x=823.
If you want a copy of the spreadsheet I made, please e-mail me.
However, I doubt that whoever set you this question expects you to have computer programming skills. I would advise you to ask your teacher for help.
I hope I have helped at least a little bit.
P.S. I am trying to start up my own homework help website. I would be extremely grateful if you would e-mail me some feedback on the help you received to adam.chapman@student.manchester.ac.uk
Adam