38. How many ways can you order a sandwich if you can order it with or? without ham, mustard, mayo, or cheese? 18 12 21 16

Step 1 ：This is a problem of combinations. Each ingredient (ham, mustard, mayo, cheese) can be either included or not included in the sandwich. So for each ingredient, there are 2 possibilities. Since there are 4 ingredients, the total number of combinations would be \(2^4\).

Step 2 ：Calculate the total number of combinations: \(num\_ingredients = 4\)

Step 3 ：Calculate the total number of combinations: \(num\_combinations = 2^{num\_ingredients} = 16\)

Step 4 ：Final Answer: The number of ways you can order a sandwich is \(\boxed{16}\).