This is probably a better question to directly ask RMC.
When you come to RMC (or immediately prior to) all your transcripts will be considered for transfer credit (including AP) by the PLAR Department (Prior Learning Assessment Request). So ensure that you send them an official AP transcript. By my experience, PLAR will probably only look at your exam score along side the curriculum of the course. From here there are a couple possibilities:
1) They will offer you credit for the first half Calculus 1, or with some luck, all of first-year calculus.
2) Normally, if a request is turned down and the credit is not granted, you will be able to write a challenge exam for the course provided you can demonstrate prior learning of it, alongside a reasonable grade. In this case the Department of Mathematics would consider your actual percentage grade and given that it is 55, it may not suffice.
AP Courses are treated as university transfer credits, however what they actually transfer to is not always so clear. Again, I would suggest inquiring with RMC directly regarding this, and soon too. In my experience you may get the credit, but they could just as easily make you repeat it.
In regards to just your general entrance average, to the best of my knowledge, consider the 55 included especially if it was taken in your senior year. The score you received on the official exam would likely not influence your entrance average, but whether or not they grant you transfer credit.
