Ladder and box (and wall)

A ladder with the length 10 m is leaned against a box (all sides has the length1 m) placed against a wall. But the ground is so slippery that the ladder falls ower the bow and leans against the wall as well. How high up on the wall does the ladder reach?

I had tried to solve this but only get a fourth order equation, and I don't know how to solve any equation of order higher than two. It seems easy but it turns out it isn't. Is the equation solvable?

By the way, my previous thread about modular arithmetic and equation systems wasn't finished, though it was marked as if it was, I happen to click on the "thank you" button by mistake. I would appreciate if someone took a look at it again, or maybe unmarked it as a finished thread. Please? :)