RSA is one of the most common modern cryptosystems, known for it's public and private key encryption. If you see public and private keys, there is a strong chance that it is an RSA problem, or at least RSA derived.
Read this: https://ctf101.org/cryptography/what-is-rsa/
Make an account for Hack the Box, an awesome place to practice your skills. Then follow this writeup and submit your solution: https://swapnil-pathak.github.io/hackthebox/walkthrough/htb-challenges-crypto-weakrsa/#.
Follow this writeup and submit your solution: https://qy.sg/x-ctf-fact0r!z3-and-fact0r!z3_aga!n-crypto/