Thank you very much Bill! I actually have been looking for decent sites, but either, like you said, are covered in a mess of ads, or are too advanced for what I need (I do want to learn calculus proper eventually, but I can't just jump in head first without the basics at a point where I am confident about them).

Fortunately, I have a skill with formula memorization, which was especially helpful with physics. So hopefully that comes back to me as well.