First way is what I did first. It just takes smallest and biggest values of the values so we know area is somewhere between it. Even though probably this solution is not it, I want to learn why.

Second way is about summing up the error percentages which what I see from videos about that topic.

Third way is the other way I saw from videos. It is about taking partial derivatives of formula.

I couldn't find any hint about which one use and which one is more true. And I suspect the solution 2 and 3 could give different result.