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 only root is -2. The roots are where the function goes through the x-axis. This polynomial goes through in lots of places, but the only answer that matches is -2
Answer:
3x + 21
Step-by-step explanation:
3(x + 7) Distribute
3x + 21