The sum of $3 + 3 = 6$.

Would you like any more details or have any questions? Here are some related problems you can try:

1. $5 + 7 = ?$
2. $12 - 4 = ?$
3. $6 \times 2 = ?$
4. $18 \div 3 = ?$
5. $9 + 15 = ?$

Tip: Always remember to follow the order of operations (PEMDAS) when dealing with more complex expressions.