Alternate interior angles on parallel lines via the parallel postulate gives you the angle supplementary to x = 120°, so x = 60°. alternate interior angles on 70° via the parallel postulate gives you y = 70°
If i'm correct you should add 0.5 mL to your 1 gallon tank, and I would say about 1.25 mL to your 2.5 gallon. It will not be extreme if you end up putting a little more in than you are supposed to. I'm not 100% because i haven't slept so my brain is being slow.
