2. You could use trigonometry to figure it out, or go to this nifty link: http://alex.phred.org/stemchart/

For both stems, use "90" for the reach, "72" for the head tube angle, and the same number of spacers.

For red, use an angle of "0" and for blue use the angle of the stem you have. It'll probably be somewhere between 7 and 35 (this is the angle the stem rises out from perpendicular to the steerer tube). If the stem is flipped, then this value will be negative.

It will tell you how much shorter reach the blue stem has compared to red; subtract this from 90mm to get the effective reach of your stem.