Maths question-Linear Functions... arrgh! Please help

3x -3-4x-8-12x+18=0???

Ok well I am having trouble understanding linear functions and how exactly they should be solved... for example

3(x-1) -4(x-2) -6(2x+3) =0

the answer to this is -1 but I dont get how its arrived at this
I know all about multiplying out the brackets first and then I believe you subtract from the RHS if its added on the LHS but some of the examples I am doing dont seem to add up?? Like sometimes they are adding when i feel they should be suntracting on the RHS??? I am soo confused. Can anyone do a step by step of the above for me fully explaining because i have spent hours on this and i am not gettin it at all.. dont know whats wrong with me!! Stressed out!! My exam is on the 10th Jan and I am feeling really out of my depth!!

3x -3-4x-8-12x+18=0???

Here's a random example; hopefully it'll help you figure out where you're going wrong. PS, the Maths help forum is here.

6(x+2)-3(x-7)-3(3x+2)=0

Multiply out all the brackets:
6(x+2) = 6x+12
-3(x-7) = (-3) multiplied by (x-7) = -3x + 21 because two negatives (-3 and -7) multiplied together gives you a positive number.
-3(3x+2) = (-3) multiplied by (3x+2) = -9x-6 because one negative multiplied by one positive (-3 and 2) gives you a negative number.

So let's put this back:

6(x+2)-3(x-7)-3(3x+2)=0
6x+12-3x+21-9x-6=0

Simplify this by collecting all the similar things together; in other words, group all your "x" and all your normal numbers together so it's easier to look at:

Collecting your "x"s together, you get 6x-3x-9x, which is -6x
Collecting numbers together, you get 12+21-6, which is 27

So,

-6x+27=0

Now what you want to do is put "x" on one side, and have numbers on the other side. At the moment, you've got both of them on one side. So, one thing you can do is add 6x to both sides.

-6x+6x+27=6x

Because -6x+6x = 0, that is the same as
27=6x
So x=27/6

Another way of thinking about this is "moving" 6x to the other side, and when you move sides, you gotta switch the sign. So negative becomes positive if you want to switch sides.

As Pheylan says, this is not quite correct.
Once you have it correct though, you need to, as said above, collect 'like' terms. ie if you had 3+4x+2+6x you'd get 5+10x. Can you see that?

Yep can clearly see where I am going wrong... i've not taken into account then negative numbers and thats why its subtracting when I feel it should be adding!! Thanks soo much