relative formula copied across worksheets:can i use the coding

I have visited this link (http://excel.bigresource.com/Track/excel-tBtBah5G/ )
as I had a problem very similiar to the one in the thread. I have followed the steps and got the programming to work. I am curious to know if I can do things a little different. My first question, can i use the coding I have in my worksheet to and also name my sheets? The only way I am able to make it work is by naming the sheets simply 1,2,3,4,etc.

Also, as you will see in my spreadsheet, I would like to drag the formula that I have written down say 20 rows. I tried to do it but noticed the last part of the formula, in this case L4, does not change as I drag. I have tried some things but can not figure out how to switch that . I have only included two rows for this example, pencils and erasers but would like to add up to 25 or more. Thanks.