need help to get average from multiple worksheets ommiting (0)@blank in new sheet

Hello

I'm new to the forum and excel. I'm using excel 2007. I need help on getting an average from multiple sheets into a sheet.
I've named the multiple sheets as WA to WA(12). and i would like to get the average from these sheets to a sheet called LE15X in the column weekly assessment. i've succeded by using this formula =AVERAGE('WA:WA (12)'!I11). My problem is, how can i get the average by ommiting the value zero(0) or blank in any the WA to WA(12) sheets.

With this I attached the sample Data. Any help is very much appreciated. TQ.