Project for Jesus Alejandro G. -- 2

I have a data table which contains values by period. The periods are text fields e.g. 2017 07, 2017 08 etc. The data for a particlular measure is defined by a field called category. I need a DAX formula that calculates the total for last rolling 12 months based on the category - then uses these totals to calculate an incident rate. Need full explanation of how formula works. Expect the solution to be a combination of calculate and filter functions. To be clear the output is a pivot table containing resulst calculated with DAX formulas. acting on the table in the example. The resut being a pivot table that looks like the second table in the example. It will need to calculate for each line the total for the last 12 months period. If it helps to add an index column to the original table which starts at 1 for the first month then this is OK. Will have other DAX issues going forward that i will need help with