The volume of a gas is 400.o mL when the pressure is 1.00 atm. At the same temperature, what is the pressure at which the volume of gas is 2.0 L?

PV=nRT

in above question:
n-->const
R=8.314-->const
T-->const

PV=nRT-->const

(1)(400mL)=P(2L)
(1)(0.400)=P(2L) find P