Issue - Complex Equasions in Flash

I am having trouble working out complex equations in flash. I am trying to work out Body Fat Percentage. The equation is:

Body Fat Percentage = 495 / (1.0324-0.19077(log(waist-neck))+0.15456(log(height)))-450

This is my actionscript:
var bodyfat:Number = 495 / (1.0324-0.19077(Math.log*(txt_waist - txt_neck))+0.15456(Math.log*(txt_height)))-450;

I might just leave it for now and then get back to it later. Not that i have much time too. I think that it is how I am structuring the equation. I am having trouble finding a helpful and relevant Help file to teach me about complex equations in flash.