Boyle’s law states that for a fixed amount of gas the pressure of gas is inversely proportional to the volume of the gas at constant temperature.
P1v1 = P2v2
Where P1 is pressure and v1 is volume at first instance
And P2 is pressure and v2 is volume at second instance
Substituting the values
3 atm x 5 L = P2 x 7.5 L
P2 = 2 atm
The new pressure of the expanded volume of gas is 2 atm
