I have to calculate pressure in psi or (lb/sqin) but I can't

P =(4gal/min)/2g + ( 25lb/sqin) -- (25gal/min)/2g

P =...

You're going to have to be more explicit - what exactly are you trying to solve? It's impossible to tell from what you wrote. I suggest you write the problem out exactly as it was given to you, and that you also show us how you tried to solve it and where you're getting stuck.