$4.$ In the PC$0\text{'}$s IP Address text box, type $192\mathrm{.}168\mathrm{.}100\mathrm{.}16.$ In the Subnet Mask text box, type $255\mathrm{.}255\mathrm{.}255\mathrm{.}240,$ and press Enter. Again, you see a message stating that the IP address and subnet mask combination is invalid. Explain why.