Gotoandplay(variable) as scene

I am working on a project with several scenes and sections of frames within these scenes which act as pages.
I have a next and back button in a movieclip. Let’s concentrate on one of them because they are similar anyway.
When you click on next, it does a function which is set in the first frame of each scene. The function is called fNext.
Everything is working ok up to now but in the function I need to specify where next is.
I decided to use a variable which I set in the last frame of every page where the palayhead finally stops. For example in scene MainMenu I have 2 pages 30 frames. Page 1 (startMain) is frames 1 to 30 and page 2 (Main) is frames 31 to 60. Scene Introduction has only one page frames 1 to 30. There are about 12 scenes.
Now when I am in scene MainMenu page 1 (startMain I set the next variable to 0 and in the functionfNext is says:

function fNext() {
if (next == 0) {
} else if (next == “stop”) {
} else {

That is working. I need to change the nextScene().
In scene MainMenu page 2 (Main), when I click next I want to go to the next scene (Introduction) and I can do it if I just use nextScene but my boss wants me to use a variable in case the scene order is mixed up.
That means I need an “else” that goes to the scene that is the value of the ‘next’ variable set in the page you are.
For example next = “Introduction”
This did not work. How can I set a variable for the scene and use gotoAndPlay(variable). If I cannotdo it is there a way round it?

I know it sounds complicated but I am greek and I don’t know how to explain it very well.

Many thanks.