Final answer:
The Caesar cipher is used to encrypt the given messages, and they can be decrypted by shifting the letters back to their original positions.
Step-by-step explanation:
The given messages have been encrypted using the Caesar cipher, which is a substitution cipher where each letter in the plaintext is shifted a certain number of places down the alphabet. In order to decrypt the messages, we need to shift the letters back to their original positions.
For example, for the message 'EOXH MHDQV', the shift is 4 letters backward. So, 'EOXH' becomes 'APIA'.
Applying the same process to the other messages, we can decrypt them as follows:
b) 'WHVW WRGDB' becomes 'STEP STEPUP'
c) 'HDW GLP VXP' becomes 'CAT DNA XYZ'