Add simple calculator

[AnshMeshram]

Title and Issue number

Title :

Issue No. : #288

Code Stack :

Close #288

Checklist:

• [] I have mentioned the issue number in my Pull Request.
• [] I have commented my code, particularly in hard-to-understand areas
• [] I have created a helpful and easy to understand README.md
• [] I have updated the Index.html file for my contribution

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[sadanandpai]

@AnshMeshram Calculator is already a part of the Mini challenges