Which maximal amount of nodes can subnet with mask 255.255.255.248 contain?

Question

Which maximal amount of nodes can subnet with mask 255.255.255.248 contain? Kindly explain how it can be calculated

Answer 1

Convert it to binary:

11111111111111111111111111111000

Invert it:

00000000000000000000000000000111

Convert to decimal:

7

Subtract 1:

6