Need help calling upon a previously stored value

[beakflop]

Hi! I am -very- new to toying with addons, so please forgive me if I term something incorrectly.

I've been toying around with TRP3 extended, and have been trying to make a battle system of sorts that uses a global variable system to keep track of things like Health, enemies defeated, etc.. I've been able to learn how to do most of what I've wanted to do by reverse-engineering the items that came pre-packaged with the addon, but I'm a little stumped when it comes to this last thing.

I set up a little system to remember the previous dice roll result via ${last.return} and storing it as "lastroll".. Doing so, I've been able to keep track of my last roll in the main quest box that the addon provides, as seen here:

https://i.imgur.com/xvK3XsY.png

However, when I try and call upon that value in the middle of a workflow to subtract it from "hp" (which is displayed in the first pic), I'm not sure what to type in.

https://i.imgur.com/ACkzREy.png -- I wrote "whatdoiputhere" for the bit I'm confused about. How do I call on the value of "lastroll" in a similar way ${last.return} does for the previous output, so I can subtract the diceroll result from "hp"? I tried ${lastroll} as well as just lastroll, but those didn't work.

I'm unsure of what code/language the addon even uses so I've had a lot of trouble looking it up myself. Everything else works fine, I just don't know what to type there. Any help would be awesome, thanks