Subtract text in one cell from another cell? Trying to split cells...

Hi,

I am sure the answer is right in front of me, but my head hurts.

I have two columns, one that has a run-on string of text (A) and another where I've extracted text from the left (B), the character length varies though. I have figured out a way to do this - as now the character length should start being consistent, but I need to take the run-on minus what was extracted and have the remaining text show in another cell (C).

I'm sure this doesn't make sense but here is what I have:
I have a run-on text string that isn't delimited and doesn't always have the same amount of leading characters, so I can't split by fixed width...

Column A: raw Text
Column B: I figured out
Column C: What I want

Column A Column B Column C
1103HYclose 1103 and 1104 task 1103HY close 1103 and 1104 task
CHGChange Couns code to CHG CHG Change Couns code to CHG
CMMOMHYchange MOM flag CMMOMHY change MOM flag

Can anyone please help me??