Put the a² over 11 so that everything on top 
and bottom will be a fraction.  I used 11 instead
of just 1 because it "stacks up" better using the forum's
notation system.  You can just use 1 where I have 11.

Look at all the denominators on the top and the bottom.
Their LCD is z³. so multiply by , written as


·
Now distribute:
     
In the upper left term you can cancel the z³'s, 
     leaving x²a.
The upper right term becomes just -z³a².
In the lower left term, subtract the exponents 
     of the z's and get simply zx.
In the lower right term you can cancel the z³'s,
     leaving -3.

So you end up with:

Now if you like you can factor out "a" on top:

but that step isn't necessary.

Edwin