Anyone know spreadsheet formulas?

[Myka]

I'm trying to figure out how to get a spread sheet to do this...

------------A-----B--------C---------D----------E------
----------Start | End | Column T | Column B | Column P--

1---------1000--1500----500---------X-------(blank)---
2---------1000--1250----250-------(blank)------X------
3---------1000--1500----500-------(blank)------X------
4
5--Total-----------------------------500-------750-----


So I want Column T to be Column B minus Column A. Then I want the Total at the bottom to add up all the Column T that have an X under the Good column, and then add up all the Column T that have an X under the Bad column. I hope this makes sense. I know how to get the formula for Column B minus Column A equals Column T. It's the second part that has me stumped.

Please help!