The /20 supernet parameter specifies that 20 of the IP address will be constant and the rest will vary. The binary version of the initial address is
The first 20 bits of the highest address must be the same as the initial address, and the rest of the address bits can vary. Show the varying bits as the opposite end of the range (all ones instead of all zeros):
The address range is 188.8.131.52 to 184.108.40.206.