Given a set S, a proper subset of S is a subset of S that is not equal to S.
To determine the number of subsets of any particular set, we use the formula below:
[tex]2^{n\text{ }}where\text{ n is the number of elements in the set.}[/tex]In the given set:
[tex]L=\{\operatorname{mm},cm,m,\operatorname{km}\}[/tex]