This is like trying to find out a 4 digit code but with only 7 numbers.
The question states that there are 4 kinds of sandwiches so we will make 4 sandwiches
salami
cheese
baloni
pastrami
We have 12 different choices of sandwich with side.
salami - chips
salami - coleslaw
salami - baked beans
cheese - chips
cheese - coleslaw
cheese - baked beans
baloni - chips
baloni - coleslaw
baloni - baked beans
pastrami - chips
pastrami - coleslaw
pastrami - baked beans
PS: did you know that there is exactly 10,000 pssible combinations in a 4 digit code with 10 numbers starting at 0000 all the way to 9999