How do you do this problem?

Asymmetric Cryptography 4. You are communicating with someone using RSA. Their public exponent is 53 , with modulus (ciock size) 143. They send you the plaintext message 20 with the signature 37. The signature should be an encrypted copy of the plaintext which they calculated using their private key: what is the equation you could evaluate. using their public information and the signed message, that must be true for the signature to be authentic