Solving for an item distribution

Hi All,

I am trying to solve for a distribution. So I have a business in which I sell a subscription of 4 more items per week. I know my average distribution of number of items per order (as seen in A3:B13) and I know this acocunts for roughly 96% of items sold. I have a special item that is an "add-on" item that is added to an order adhoc. Before adding this ad-hoc item to an order, I know my average items per order is 5.84, since this accounts for 96% of all orders I know my expected average items per order is closer to 6.10.

How can I back-solve for those item distributions. So once the upgrade is done, how many people fall into each of those buckets. The ad-hoc item is actually 2 items (only numbers divisble by 2 can order it), so if I am 4 item plan and I add this add-on item, I have 6 items being shipped to me.

Thanks so much for the help!