How do I change a shadow's opacity in relation to another object?

Well, I already know how to do the first bit. I've got a shadow and it measures the distance to its owner and sets opacity according to that value. The bit I'm getting stuck on is that it's working in the reverse as to how I want it to happen. Basically, the closer the object, the darker the shadow should be, not vice versa. Added a gif to demonstrate.

And here's the code:

I feel like I need an expression that can take a number and flip it within a range of 100. So 3 becomes 97, 30 becomes 70 and so forth. But I don't know how to do that or if it's even feasible.

TIA

lol, I'm such a dork. The answer was in my question.

Just added a second variable which is the difference between 100 and distanceToOwner and set opactiy to that. Sure enough, it works.