The polynomial is degree 1, so you'll need at least 2 points to find it
Once you get the value of f(0), go to rip-demo.andrewkdinh.com/f(0)
Here's resources with more information. Password should've been given to you
Decryption key: echo "U2FsdGVkX1/fG6A2L6D50C2kCsrMw/sVdrjxJF7SfLy5z/92gR3So4LXBm8CYl3K"|openssl base64 -d|openssl enc -d -pbkdf2 -aes-256-cbc -k "PASSWORD_HERE"
Some other tools to do Lagrange/polynomial interpolation:
Source code available on GitHub and Gitea
Licensed under AGPL 3.0