When a certain air-filled parallel-plate capacitor is connected across a battery, it acquires a charge of 150

Question:

When a certain air-filled parallel-plate capacitor is connected across a battery, it acquires a charge of 150 µC on each plate. While the battery connection is maintained, a dielectric slab is inserted into, and fills, the region between the plates. This results in the accumulation of an additional charge of 200 µC on each plate. What is the dielectric constant of the slab?