1) list your givens
P = ?
V = 7.00 L
n = 3.00 mol
R = 8.314 [tex]\frac{kPa\ L}{mol\ k}[/tex]
T= 300.15 K
2) rearrange your formula
[tex]PV=nRT\\\\P=\frac{nRT}{V}[/tex]
3) solve
[tex]P=\frac{(3.00\ mol)(8.314\ \frac{kPa\ L}{mol\ k})(300.15\ K)}{(7.00\ L)}\\\\P=1069.4773299[/tex]
[tex]P=1.07[/tex] × [tex]10^{3}\ kPa[/tex]