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As dflak says " if you have Excel 2013, then why is this spreadsheet in XLS format?"

I would just add one thing to the Pivot table that dflak created and that would be a Subtotal for the years. Otherwise, my solution is identical to dflak's.

Sheet4 has the pivot table with the subtotal for each year. (right click on the years column and choose Subtotal "Years".

Charting is also possible using the data from the Pivot Table.

I also don't understand why you have a worksheet for each month. List everything in one long list.