>How do I make X the subject, if 'X' appears on both sides of the '='
You have to find a way to get all the x's on the same side. Some forms are easier than others.
>... for example 2X = 6X over 5Z + 8Z
That is (using lower case)
2x = 6x/(5z + 8z)
Well first of all those terms in the bottom can be combined.
2x = 6x/13z
Generally when you have a fraction, you're going to want to multiply by the denominator so it's not a fraction any more. So multiply both sides by 13z.
26xz = 6x
Now, finally, you can move all the x terms to the same side. Let's subtract the 6x from both sides so you no longer have an x on the right.
26xz - 6x = 0
And you can factor out an x
x(26z - 6) = 0
And you can divide both sides by the thing in parentheses
x(26z - 6)/(26z - 6) = 0/(26z - 6)
x = 0
To summarize, when you have fractions involved, it's often this process
* Clear fractions by multiplying by the denominator
* Move all the x terms to the same side
* Factor out the x
* Divide by the thing multiplying x
Feel free to ask with more complicated examples.