I took Calc I at Washtenaw last summer. At some point, you need to “apply” to Washtenaw as a visiting student. This can just be done through their website. After a couple days, you should receive an email from them once you are accepted. Once you are accepted, you can register for classes on their website too. Enrollment for the Spring/Summer is already open, and classes typically fill up pretty quick for the summer because a lot of Michigan students take classes there. I know last summer all the Calc I classes filled. So, I would do this as soon as possible if you are planning on taking Calc/Physics.
Hope this helps! If you have more questions, feel free to respond to this post or attend our advising hours.
-Cate, PMH Co-President