Encrypt and Decrypt message Cryptography

Refer to the following correspondence between the set {, , , . . . , , , !, _} and the modular set 28 under the operations addition and multiplication modulo 28:

A 1, B 2, C 3, . . . , Y 25, Z 26, (space) 27, ? 0;

Use the equation = 5 + 10 (modulo 28), to: (a) encrypt the word plaintext "CAN YOU ENCRYPT THIS?"; and (b) decrypt the hidden message "M NNEWACENGOHGEWACPEYASLAPZE?AXGJ"

Please show me a solution, thank you!