How calculate difference of columns in MATRIX visual, between 2 months not in sequence ?

Hi ... there is always a new challange in PBI, isn't !?😅😅

Here we go ... see this simple matrix:

1 - How could be calculated the difference of sales between those two filtered months (not sequenced), for each product item ?

2 - How could be displayed that last column DIFFERENCE ?

Thanks all ... a lot !!!