C I think sorry I will try I will get other answers later
Answer:
The solution is 
Step-by-step explanation:
You are given the system of three equations:

Multiply the first equation by 4, the second equation by 3 and subtract them. Then multiply the third equation by 2 and subtract it from the second equation:

So,

Multiply the third equation by 23 and subtract it from the second equation:

Hence,

Substitute it into the second equation:

Substitute them into the first equation:

The solution is 
Yes, a trinomial is also a polynomial.
Answer:
6x+3x=9x
2+7=9
9(x+1)
Distributive property
9x + 9
(im not completly sure this is the right answer)