A service call charge or fee is when you are charged a certain amount of money in order for a service technician to perform that specfic service.
For this case we have the following expression:

We follow the steps below:
We subtract 4x on both sides of the equation:

We subtract 10 from both sides of the equation:

Now, we must complete squares.
When we have an equation of the form:
, if we want to complete squares we must subtract c on both sides of the equation obtaining:

The square is completed by adding to both sides of the equation: 
So, we have left:

In the given expression we have:

And to complete the square we have:

Rewriting we have:

We factor the left side of the equation, that is, we look for two numbers that when added together result in -8 and when multiplied as a result 16. We have:

So, we have:

Answer:
The intermediate step is to complete squares

The second choice is correct. Given that angle 2 and angle 6 are congruent, the largest in each of the corresponding triangles are vertical angles meaning that two known angles are known in each triangle (and they are equal) which means that the last "unknown" (angles 3 and 7) are congruent. The lines DC and AB correspond with these defined, congruent triangles meaning they are parallel.