I imported a vm into Oracle VirtualBox that was exported from VMWare ESXi and found the only resolution to use was 640×480.
To solve open a shell and run apt-get install virtualbox-guest-dkms
Kudos to askbuntu.com
Subnetting a class C address in your head
In our example we apply the subnet mask 255.255.255.128 [ /25] to the network 192.16.11.0.
Subtract 25 from 32 total mask bits to leave 7 unmask bits which give way to host bits. Find the total address, including subnet and broadcast, per subnet chunk by raising 2 to the power of unmask bits.
Remember 2^8 = 256
2^7 = (2^8) / 2 = 128
Count from 0 by increments found in your computed answer to 256.
In this case we established two subnets using the /25 netmask.
Subnet First Host Last Host Broadcast
0 1 126 127
128 129 254 255