You have a lot of questions here, I can help you with a few of them.
When you simplify the polynomials, you put together all of the terms that have the same degree. That means the variables have the same exponents. The number of terms are the items separated by plus and minus signs.
Here are the answers for the first three:
1)

2)

3)
Answer:what
Step-by-step explanation:
Answer:
x +3
Step-by-step explanation:
You can solve this by factoring.
The numbers have to add to 10 and multiply to 21.
The first numbers that should come to mind are 7 and 3
(x+3)(x+7)
x+3 is the shorter side and there you go :)
The slope equation is y=mx+b where m is the slope and b is the y intercept. After plugging the numbers into the equation you should get y=-2x+6. Hope this helps!