Update Last Question In mux-demux.md

[ArnabC27]

A meaningful title for PR, not like: made changes to xyz.md

Fixes #

Ref #

Changes done:

• [x] Task 1

Screenshots

Preview Link(s):

✅️ By submitting this PR, I have verified the following

• [x] Checked to see if a similar PR has already been opened 🤔️
• [x] Reviewed the contributing guidelines 🔍️
• [ ] Sample preview link added (add the link(s) for all the pages changed/updated from the checks tab after checks complete)
• [ ] Tried Squashing the commits into one

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[manjotsidhu]

Can you explain your changes and issue it fixes ?