Follow these steps:
Find the initial pressure. We will take atmospheric pressure at sea level: Pi = 1 atm = 101,325 Pa.
Find the final pressure. In a cruising plane, the cabin is usually pressurized at about Pf = 0.8 atm = 81,060 Pa.
Calculate the final volume with Boyle's law: Vf = Pi · Vi/Pf = (101,325 Pa · 0.001 m3)/81,060 Pa = 0.00125 m3.
Find the expansion by subtracting the final and initial volumes : ΔV = Vf - Vi = (0.00125 - 0.001) m3 = 0.00025 m3 = 250 cm3.
Read more