Firstly, this is not my homework. I am well past high school (finished graduate school several years ago) but I am mentoring a high schooler and I want to explain how to solve this by hand using just pen and paper.
A more presentable form + solution is here
My own attempts could only simplify it to a fourth degree polynomial in $x$ and equate it to $0$. There's gotta be a better way but it is beyond me and I feel embarrassed!