What is this pls help

8 - 4 = 7 - 3 because it has a equal sign in the middle meaning that you have to find an equation that’s equal to it. So thats why the missing number is 3

3
are you serious? If you are, here’s the explanation:
It’s like finding x
8-4=7-x
Let’s simplify it, we know that 8-4=4
4=7-x
Now, we wanna get x by itself, since that’s what we’re looking for.
Go ahead & get rid of 7. Since 7 is a positive number, well subtract it. Also, remember that what we do on one side, we must do to the other side, so subtract 7 on BOTH sides
4-7=-x
Simplify.
-3=-x
Now, we need x to be positive, so let’s get rid of the negative sign (-).
We’ll do this by dividing -1 on BOTH sides.
3=x ——> x=3
Hope this helps! :)