1. (2x-6)/(21) divided by (5x-15)/(12)

2. Solve (x)/(x-9)-4=(9)/(x-9)..I got -6, is that correct?

3. Add. Express your answer in simplest form...(4)/(s)+(6)/(s^2)..

4. Add. Express your answer in simplest form...(x^2)/(x+4)+(8x+16)/(x+4)

Lets check you number 2)

-6/(-15) - 4= 9/(-15)
6/15-4= ?
-3 7/15 does not equal -9/15

Show your work. You wont find many here that will do these for you.

On question #1, you multiply the first number by the inverse of the other.

So what's:

(2x-6)/21 * 12/(5x-15)

Question 2 seems impossible to me. But I might be doing it wrong...it's almost midnight here.
I subtracted the (x)/(x-9) on both sides and came up with the equation:

-4 = (9-x)/(x-9) No matter what you plug into there, it will be -1. And
-4 does not equal -1.
Wait for someone else's confirmation on that though.

On question #3, here's a hint. If you multiply something by 1, it will still stay the same. s/s = 1. See what you can do with that.

#4 - add the numerators straight across. You MAY be able to factor it out and get rid of the denominator. You'll have to try it out to see.

As you post your work, we can critique it.