You'll note that there are a lot of similarities between
The shape of the 8 and the shape of the 3.
So what the equation is saying is that
If we visually take a 3-shaped curve out of the 8-shape, we're left with a 7.
Question is very vague and I have asked OP to clarify in a comment to the question.
Meanwhile, I think to solve an "equation" we require an "unknown".
Here, the 7 is not a 7, rather it is part of a question mark "?" which is the "unknown" in the "equation" and hence 8-3=? is 8-3=5.
Similarly 8+3=? is 8+3=11.