Briefly describe how to calculate subnet masks.

What will be an ideal response?

There are several varieties of subnet masks that you can design for a network, depending on how you want to implement an address segmentation scheme. The simplest form of subnet masking uses a technique called constant-length subnet masking (CLSM), in which each subnet includes the same number of stations and represents a simple division of the address space made available by subnetting into multiple equal segments.
Another form of subnet masking uses a technique called variable-length subnet masking (VLSM) and permits a single address to be subdivided into multiple subnets, in which subnets need not all be the same size.