The simplest way to calculate VLSM is by using a subnetting chart like the one shown in Table 3.0 above, and then following the steps below:
Arrange the requirements of IP addresses in descending order like the one shown on Table 4.0 above
Using the subnetting chart, assign the appropriate subnet masks to each subnet based on the required number of hosts.
Allocate one the resulting subnets to the designated LAN  and reserve the rest for future use
Pick the next available subnet from step 3 above, and repeat the subnetting process using the chart till you get to last network on your list
Review and document your subnetting summary
Please see the “Implementing VLSM Subnetting” section above for detailed explanation.