Two spies have to communicate using a secret code. They need to create exactly 30 possible precoded messages, using a single number and letter. Which structure should the code have? Select a number from {1, 2, 3, 4} and a vowel. Select a number from {1, 2, 3, 4, 5} and a vowel. Select a number from {1, 2, 3, 4, 5, 6} and a vowel. Select a number from {1, 2, 3, 4, 5} and a consonant.