Another similar triangle problem

Regarding similar triangles, most of the students can memorize the rules. However, they don't know how to apply the rules to solve problems or they even don't have the sense to realize that the problem is about similar triangles.

Let's take look at the following problem from the official practice test.

From the figure and the information in the question, we can draw the figure below:

Triangel ABD is similar to triangle BCE because they are right triangles with ABD = BCE. So, we only need to find CE. Because of similar triangles, we know AD/BD = BE/CE. And you have AD=5, BE = 7 and BD = 7-5 =2. Therefore, CE = 7*2/5 = 2.8, and x = CE+EF = 2.8 + 7 = 9.8. 

Easy, right?