From the table it can be seen that the pressure at 8000' is 10.92 psi
Now we've been told because of the crack in the cabin window we can
maintain a pressure differential of 5psi. Therefore the air outside can only be 5psi less than that inside the cabin. ie
10.92 - 5 = 5.92
Again from the table the altitude where we get closest to 5.92 is
approximately 23000' (FL230)