Angles and sides of a triangle?

I need help with a formula. This is why.

I have a roof pitch of X:12 and a variable truss heel height that I can define by my program. Problem is the program defines the heel height to the bottom of a 3 1/2" truss member and not the top. I want the top to be 14", so what would the bottom have to be at? To know this, I need to know the vertical height of a 2x4 at the angle defined by the roof pitch. I have laid this out on a diagram where X is the rise of the roof, and I must solve for Z. I haven't done any Trig in 10 years and I got a headache just trying to think of a formula. Can anyone come up with a formula that can be placed in Excel where I just have to enter a new value for X and get the value for Z? My diagram can be viewed here:

http://www.northernscribe.net/TRIANGLE.PDF

Thanks