Using object (?) types in Math Expression

In a Math Expression, you can put in variables that aren’t numbers, like my pc_manager blueprint here; however, I have no idea what the syntax is to get that object’s variables, like to the right.

Basically what I’d like to write on the expression is something like

pc_manager.landUsed+bp_reactorFission.landTaken

But of course that syntax is not correct and will result in an error. I haven’t found an official doc for understanding the math expression syntax for something like this.

I know I can get around this by typing “x+y” in the Math Expression and just setting up the inputs as so:

But this is of course a waste of time, since I’ve done the exact same thing just underneath just using int+int.