Idon't want a simple answer. i want to know how to do it.

The image is a bit hard to make out, so I'm going to make some guesses. It looks like it says , , and , and you're asked to find .

You know that and are similar, which means their corresponding sides are proportional in length. So there's some constant such that





To find , you need to know and the constant .

Clearly, . So, the first equation becomes



Then in the second equation, you have