Modify report to show calculation

Hi Everyone,

So it's been a while since I've had to modify a report and I'm having a brain block right now... I've been asked to modify report 99000784 to show on each machine line the total capacity that is 90days past due. Not each individual Production order but the total capacity (time) that is "past due"

Currently the report gives the effective capacity, and how much capacity is needed for Prod. Orders and then what's available...

I'm looking for direction on how to tackle getting the total time of what is past due from the day that is ran in the starting date minus 90days where the routing status for that machine center is not = to "Finished"

Thanks for any advice or recommendations on where to start... At first I was thinking I could use the "Prod. Order Need (Qty.)" variable to to reverse that and subtract the PeriodStartingDate by 90 days but it didn't work.

Thanks!