From Boyle's law, we can use the equation
P1V1 = P2V2
to find the volume when the pressure is increased to 760 kPa:
V2 = P1V1 / P2
V2 = (210 kPa)(15.0 L) / 760 kPa
V2 = 4.14 Liters
Therefore, the volume is 3.99 Liters after the pressure increased to 760 kPa.
But if the pressure is increased to 790 kPa, the volume of the krypton will decrease to
V2 = P1V1 / P2
V2 = (210 kPa)(15.0 L) / 790 kPa
V2 = 3.99 Liters