How do i move backwards?!

So I want to drive forward with RT on the Xbox and backwards with LT I have the forwards drive down but how do I do backwards drive?

Do the same as you did with the right trigger, but do it with the left. Add those values and put it in your teleopdrive.

I usually use raw axis. My final drive code looks like this.
drive.arcadeDrive((-xbox.getRawAxis(2) + xbox.getRawAxis(3)), -xbox.getRawAxis(0));

The negatives are there only for directional purposes.