Your friend and his family stays in one of the hotels in Legazpi. The hotel provides a vault where they can keep their valuables. Your friend has set a 4-digit code to lock the vault. Later, he realized that he forgot the 4-digit code. He only remembered that the code contains the digits 2, 4, 6, and 8. He is asking now for your help. How can you help your friend? How can you apply your knowledge of permutations and/or combinations here?