He i’s smart

If a smart person said it, maybe that's how it's supposed to be spelled. What are your credentials to dispute it?

How can we with that big red circle around it.

Low-tech typo.

I’m moderately impressed that they used punctuation at all, I’ll let it slide

Usually the pointer is the blahblah the teacher was droning while you were fantasizing about the attractive classmate sitting directly in front of you

I suppose “by definition” would probably have been counted as wrong

I'm thinking maybe "Because if you subtract 40 from my number you get a negative number," but I could be either over- or under-thinking it.

Yeah, I always felt like I was either pointlessly restating the obvious or it expected me to derive the damn thing from first principles.

Arbitrary glyphs can mean whatever we decide they mean. One day 8 could mean what we commonly consider to be 2 today - we just have to choose for it to be so.

The question is intended to create an existential crisis and gaslight the pupils. How can anyone truly know anything?

Probably a number line? Draw a line to show it's only 2 jumps to 20 but 4 equally spaced jumps to 40.

As a teacher that's what I would've done at least. Number lines are quite effective at helping kids visualize numbers.

This response doesn't seem to indicate this particular teacher has adequately explained what the expected answer is though.

"Because 20 - 40 is negative."