How do you find the value of x in a pair of similar polygons?

To prove similarity, corresponding angles must be the same, and also the ratio of the corresponding sides must be proportional, meaning a/b and c/d must get the same value.

So, if x is an angle, you will get information like 2 known angle values and one unknown angle value, or all three known angle values.  angle a= angle b

If x is an length, you will get three sides of any polygon being proportionate to the corresponding sides of another similar polygon or only two pairs of corresponding sides  a/b=c/d