I forgot what the Chemistry Law is called but you use (P * V) / (T) = (P * V) / (T). I believe this is the Combined Gas Law. You plug in your numbers:
(100 kPa * 2.50 L) / 303 K = (90.0 kPa * 3.75 L) / x
You'll be solving for "x" so just cross multiply, then get "x" alone on one side to get your answer. Hope this helped!
