Your second line is not correct
which leads to and
It took me 2 days, but I finally got to the point I am at (see attachment) and now have been asked to solve for C1. I feel like I should cross multiply, but when I do that I get confused and I don't think I am doing something right. I need to get C1 to the left and everything else to the right, correct? But I can't figure a way of doing that-I think I've spent too much time on this problem!
Thanks for any guidance!