Q$1$: Give a regular expression presenting each of the following languages over ${\displaystyle \underset{?}{\overset{?}{}}}=\{0,1\}$ :

a$.L_1=\{0,1^n|n3\}.$

b$.$ All strings represent even binary number less than $7.$

c$.$ All strings with no more than three $0\text{'}$s