For this challenge, you only need to know how does RSA works. And a beautiful website named dcode.org.

We have all the information to decrypt the ciphertext:

ciphertext (better to ave something to decrypt...)0x4748303c3f211ce373d68b960278f7e76a2152c9ed25559caebf5dc348d

Public Key E : 1337
The 2 prime numbers which are the factors of the key : 209258918746127467720145276363318243 & 287635494567303317074372323571608281

With that information, go to RSA-cipher page and just fill the gaps !

And then you have your flag !