Calling all math wizzes! Could I please have a bit of mathematics help with...

[llamahorse]

...this Algebra 2? I picked out all the problems and sequences of problems I wasn't sure of.. I'd appreciate any help you can give, preferably all but whatever you can will also suffice! If you could show the work for me so I can deduce what you did, or explain to me in writing what you did it would also be much appreciated! Thanks much!!! here are the problems.. they're pretty hard. =/

(find the domain of the function with the given rule.)
x² -9
1. f(x) = --------
3x+15

x²-5x
2. f(x)= -------
x²-7x+12

3. find the zeros of the function in #1

4. find the zeros of the function in #4

(simplify each rational expression)

5. (2x+5)(x-4)
--------------
(x-4)(5+2x)

6. 3x-15
--------
6x-30

7. 4x
---------
8x²-8x

8. 2x³-4x²
---------
6x³

9. a²+4a-12
-------------
3a²-12a+12

Thanks very much for everything! again, all help is greatly appreciated!