Pythagorean
Theorem as follows: A^2+B^2=C^2
If the triangles are similar, the proportion of the legs on the left to the legs on the right will be equal. This proportion would look like:

(You needed to combine the orange segment and the yellow segment to find the total length of the large triangle).
Now, cross multiply and solve for x:
28x+14=30x
<em>*Subtract 28x from both sides to isolate the variable*</em>
14=2x
<em>*Divide both sides by 2*</em>
7=x
Hope this helps!!
When you have a point A and then transform it using a linear transformation (like rotation, reflections, etc.), we mark it as A' to say, "This is the point which corresponds to A after the transformations were applied". This establishes a link between the two, even though they may appear to be unrelated to someone looking at the graph.