It's not an equation, it's simple math, like one used in a grocery store. You have 2 apples and then you pick up 4 more pairs of apples, how many apples you got?

As I said, it's not quantum mechanics, it's basic simple math.

I bet your alarm clock app also uses simple math problems like this one. It's expected for a grown up or a teenager to be able to solve this, that is why they put it on alarm clock app. It's not something that's meant to be easily forgotten. That is why you learn these things when you're very young, so they stick with you for the rest of your life. But from the answers, it's easy to notice that most have never even learned this in the first place, at all. Why? Your guess is as good as mine 🤷.