Regular expressions is a medium rated room by concatenate. I will only be posting the answers here as the creator of the room has done an awesome job of explaining about the regular expression on the room. So I suggest you to play with regex on the room on your own before looking the answers.
Task 1 - Introduction
Task 2 - Charset
Task 3 - Wildcards and optional characters
Task 4 - Metacharacters and repetitions
Task 5 - Starts with/ ends with, groups, and either/ or