It would be 4 because, on the right, it has 3 and 4. That is 7 and if you look at the scale it's balanced which means it would be the same on that side but it already has 3 so 4. So hold up your fingers and take 4 fingers up and add 3 fingers to that 4. How many is that? Count them all up and you'll get 7!
N+3=7. To find n, you need to have it by itself, so you can do that by subtracting 3 on both sides, so it would look like: n+3-3=7-3. Then you have n=4.
