I've managed to get the problem down into a simple equation, but I'm not sure if it's even possible top solve. I don't think I have enough information to do it. I need to solve whatever "A" is in order to find "X" and "Y".

A - B = X, C - A = Y. I always know B and C, but not A, X, or Y. C is always a larger number than B. We usually have A, but I need to depend on the shift before me to get me that number, or get someone with access to past numbers to get it for me. It frequently ends up that I'm the only person on duty, and can't get the number for A. I'm wondering if there even is a way to get it, or if I'll just have to keep leaving blank paperwork forever.

I've used some example numbers to make it more easy for me to look at, but it's not helping. I'll leave it here if it helps.

A - 50 = X, 100 - A = Y

Can this even be solved for A?