Question

A sample of gas is in a 50mL container at a pressure of 645 for and at a temperature of 25C

Answer 1

I'm assuming you're being asked to find moles, since that's the information you're missing here.
Use the ideal gas law formula: \(\sf \color{blue}{PV=nRT}\)
rearrange to solve for "\(\color{blue}{n}\)" since that is moles
P = pressure in atm
T - temp in kelvin
V = volume in litres

this is simple algebra.