Consistent abbreviation of pounds

[siwelwerd]

Closes #758

[github-actions]

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• source/precalculus: https://e79e955a.tbil.pages.dev/preview/precalculus
• source/precalculus/source/01-EQ/02.ptx: https://e79e955a.tbil.pages.dev/preview/precalculus/EQ2.html
• source/precalculus/source/03-LF/07.ptx: https://e79e955a.tbil.pages.dev/preview/precalculus/LF7.html
• source/calculus: https://e79e955a.tbil.pages.dev/preview/calculus
• source/calculus/source/06-AI/05.ptx: https://e79e955a.tbil.pages.dev/preview/calculus/AI5.html
• source/calculus/source/06-AI/07.ptx: https://e79e955a.tbil.pages.dev/preview/calculus/AI7.html
• source/precalculus/exercises/outcomes/LF7: https://e79e955a.tbil.pages.dev/preview/precalculus/exercises/LF7/
• source/calculus/exercises/outcomes/AI7: https://e79e955a.tbil.pages.dev/preview/calculus/exercises/AI7/

[github-actions]

🚀 Preview available 🚀

https://dae7f4f7.tbil.pages.dev

• source/precalculus: https://dae7f4f7.tbil.pages.dev/preview/precalculus
• source/precalculus/source/01-EQ/02.ptx: https://dae7f4f7.tbil.pages.dev/preview/precalculus/EQ2.html
• source/precalculus/source/03-LF/07.ptx: https://dae7f4f7.tbil.pages.dev/preview/precalculus/LF7.html
• source/calculus: https://dae7f4f7.tbil.pages.dev/preview/calculus
• source/calculus/source/06-AI/05.ptx: https://dae7f4f7.tbil.pages.dev/preview/calculus/AI5.html
• source/calculus/source/06-AI/07.ptx: https://dae7f4f7.tbil.pages.dev/preview/calculus/AI7.html
• source/precalculus/exercises/outcomes/LF7: https://dae7f4f7.tbil.pages.dev/preview/precalculus/exercises/LF7/
• source/calculus/exercises/outcomes/AI7: https://dae7f4f7.tbil.pages.dev/preview/calculus/exercises/AI7/

[jbunn3]

I'm sorry that I've been so slow to respond. The last few weeks have been a bit wild, and it just doesn't let up. I will try to carve out some time Saturday to do some reviews.