Added hex2dec

[karandeepSJ]

Closes #theRelatedIssueNumber

• [] Running yarn lint does not trigger any linter errors
• [] The test of the method you have fixed is passing
• [] You have written a new skeleton method for someone else to work on!
• [] You have written tests to accompany your skeleton method

[BlakeGuilloud]

Please review our Contributing Guide before submitting pull requests. Thanks