I was trying on this problem. All information is in picture. The aim is to find $AB$. It looks very simple problem. I spent more than one hour to solve it but I can't. It looks simple,but equation are not independent.
Is there any constructive hint? (or solving method)
There's not enough information in that picture to find any horizontal distance. If you have a situation that matches the information there, you can stretch or shrink it horizontally by any (nonzero) factor you'd like, and it would still match the information.