The last significant item to learn about VLSMs in this lab is to calculate various properties of subnets that use VLSMs$.$ Calculating these properties is similar to calculating the properties of subnets that use a fixed length subnet mask.

Let us take a look at an example. Imagine that an organization is assigned the block of addresses defined by $99\mathrm{.}216\mathrm{.}0\mathrm{.}0/13.$ The organization initially must support $100$ hosts on the first subnet, and $13$ hosts on the second subnet. Using VLSMs$,$ it creates the network identifiers as follows.

First Subnet: $0110001111011000000000000$

Second Subnet: $0110001111011000000000001000$

After some time passes, the organization needs a third subnet that supports $100$ hosts, and a fourth subnet that supports $29$ hosts, which the organization allocates. The four subnets$$ network identifiers are as follows:

First Subnet: $0110001111011000000000000$

Second Subnet: $0110001111011000000000001000$

Third Subnet: $0110001111011000000000010$

Fourth Subnet: $011000111101100000000000101$

We can now answer the following series of questions about the fourth subnet allocated. Though we focus on the fourth subnet, these questions can be answered for any of the subnets following the same methodology.

a$)$ How many bits are used by the subnet identifier of the fourth subnet?