Answer;
New tire pressure = 214.286 kPa
Explanation;
According to Boyle's Law the volume of a fixed mass of a gas is inversely proportional to pressure at constant temperature.
P α V, and PV = Constant
Therefore;
P1V1 = P2V2, where P1 is the initial pressure, V1 is the initial volume , P2 is the new pressure and V2 is the new volume.
P2 = P1V1/V2
= (300 kPa × 30 L)/ 42 L
= 214.286 kPa