Well, first, you need to find the square root of the two numbers. To find it, they are the numbers multiplied by each other to get a product. Example: The square root of 49 = 7. Why? Because 7 times 7 = 49. You see how we multiplied 7 by its own self, and how we DIDN'T multiply 7 by any other number BUT itself? See, that's how you find the square root. So, we know that 3 times 3 = 9, and THAT means the square root of 9 = 3. All we have to do now is solve the problem when it says to multiply both of the numbers, (7 times 3), and WHAT DO YOU GET? 21! (Get it? Like the 21 joke-trend?) :D (Laughing emote). :P
Final Answer: 21. :-)