I am pretty sure that B is the answer
The two pieces are continuous for every 
So, our only concern is to make sure that the pieces "glue" continuously at x=7.
To ensure this, we evaluate both pieces at x=7, and impose that the two values are equal.
The first piece evaluates to

The second piece evaluates to

So, we want

We move all terms involving c to the left hand side, and all the numerical constants on the right hand side:

Answer:
(-∞, ∞)
Step-by-step explanation:
Given,

Then (fºg)(x) would be ,

Since this is a polynomial, we know domain of a polynomial is all real number.
Therefore the domain of this (fºg)(x) is (-∞, ∞).
Yes, because if you would draw 2 parallel lines in 3D space, a plane would exist between those two lines.
Hope this helps :)