AWS Certified Cloud Practitioner - Essentials Course - 2021

34. Networking Fundamentals - II; time stamp 4.50

Would be kind enough to submit the link for the sun-net calculator. Secondely how to calculate this manually?

The link is visible in the URL bar itself. https://www.subnet-calculator.com/. To understand the whole subnetting and getting the idea of calculating it, you have to study it. A good link is Subnetting Tutorial - Subnetting Explained with Examples

2^0=1
2^1= 2
2^2 = 4
2^3 = 8
2^4= 16
2^5 = 32
2^6 = 64
2^7 = 128

if you understand subnetting then you also understand that this is useful. LOL

And this is also useful.
https://www.stationx.net/ipv4-subnet-cheat-sheet/