Answer : The new volume will be, 1.5 L
Explanation :
Boyle's Law : It is defined as the pressure of the gas is inversely proportional to the volume of the gas at constant temperature and number of moles.

or,

where,
= initial pressure = P
= final pressure = 2P
= initial volume = 3.0 L
= final volume = ?
Now put all the given values in the above equation, we get:


Thus, the new volume will be, 1.5 L