Car Game Speed

Ok, here’s my problem:
I made an Input textbox, and whatever number you put in, it adds to the speed… but I can’t get it to work… can someone help?
[AS]onClipEvent (enterFrame) {
if (Key.isDown(Key.UP)) {
speed += ymph
}
}[/AS]
That’s my car’s code.
And the Input Box’s variable is ymph
Any help deeply appreciated!