Move/Resize window problem

Please help to achieve the following in the window Move/Resize action:

Three windows, the first at the left has a fixed width (334 px).
The remaining screen width should be split between the other two windows.

(maximum.screen.width - 334)/2

How can I calculate/enter the positions for window 2 and window 3 in two Move/Resize actions? They should work at different screen resolutions.

Thanks, Hans