I have been trying to solve a physics problem with a friend of mine and we've tried every equation we can find from our notes, and we can't seem to get it, hopefully you all can help.

Scenario:

A parallel-plate capacitor has a capacitance of C = 6.50pF when there is air between the plates. The separation between the plates is 2.90mm .

Part 1:

What is the maximum magnitude of charge that can be placed on each plate if the electric field in the region between the plates is not to exceed 3.00×10^4V/m ?

Part 2:

A dielectric with a dielectric constant of 2.80 is inserted between the plates of the capacitor, completely filling the volume between the plates. Now what is the maximum magnitude of charge on each plate if the electric field between the plates is not to exceed 3.00×10^4V/m ?

Any help would be much appreciated.