$1.$ Determine the default network mask for the following IP host addresses:

$[3]$

$64\mathrm{.}1\mathrm{.}4\mathrm{.}5\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$

$197\mathrm{.}3\mathrm{.}2\mathrm{.}6\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$

$154\mathrm{.}1\mathrm{.}1\mathrm{.}1\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\text{'}$