The expression "3 + 3 + 3 + 3" represents a simple addition problem. It consists of four instances of the number 3 being added together. When you add these numbers, you can think of it as combining groups of 3. To find the total, you can add them step by step: first, 3 plus 3 equals 6, then adding another 3 gives 9, and finally, adding the last 3 results in 12. Therefore, the sum of "3 + 3 + 3 + 3" is 12.