Answer:

You should also try solving it yourself to make sure I did not make any mistake.
Step-by-step explanation:
We already know the slope so, so far the equation should look like this.

Now we just need to insert the point into the equation. So point (7,9) 7 should replace the x and 9 will replace the y. It will look like this:

when you solve this equation you'll get b

So the equation is

The number halfway between 200 and 300 is 250

If I understood correctly and didn't make any mistakes...
That would be called the quotient.
Option 3, is correct.
Just find the one that have the x's only, not the one that is squared or without one. It doesn't matter if the term is a negative or positive.
If you have any further questions, please reach out to me :)