Matrix Report

I am trying to create a matrix report.  I want to show the time taken to close a issue on different products and number of issues closed on those products in between a time frame. So i used years as rows and product as columns in data i used issue count and time. Now i want to see the total issue count , so i added subtotal on years and i am getting total number of issues closed per product. Now i am also getting total of duration as well.  And the total of duration that i am getting is wrong.  So how can i get the correct total of duration. or is there a way that i can only do sum of issue count?
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