To make the numbers 3, 3, 5, and 9 equal to 7 while using each number exactly once, you can use the following mathematical operation:

$\frac{9 - 3}{3} + 5 = 7$

Here's how it works:

1. Subtract: $9 - 3 = 6$
2. Divide: $6 \div 3 = 2$
3. Add: $2 + 5 = 7$

So, $\frac{9 - 3}{3} + 5 = 7$.

Would you like more details or have any questions?

Here are 5 related questions:

1. How would you use a similar approach to solve a different set of numbers to equal a target number?
2. Can you find a different operation with the same numbers that also equals 7?
3. What other combinations of basic operations could be used in puzzles like this?
4. How does order of operations affect the solution to this problem?
5. What are some common strategies for solving these types of number puzzles?

Tip: In puzzles like these, it’s helpful to experiment with basic operations (addition, subtraction, multiplication, and division) and consider the order of operations carefully.