FIX: aligned and general tidy up for new Monetary Lectures

[mmcky]

This PR

• [x] fixes some spelling mistakes
• [x] fixes aligned use which needs to be inside an equation environment such as $$
• [x] removes conversion markup
• [x] minor changes to spacing for readibility

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[HumphreyYang]

Many thanks @mmcky. The changes look great to me. I will have another look once the build is available.

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🚀 Deployed on https://65feac1a159c7fe3f4cec120--taupe-gaufre-c4e660.netlify.app

[mmcky]

thanks @HumphreyYang