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Algebra does use numbers. I learned to move the numbers to one side and the variables to the other.

10x+7 = -2x+31

Move 7 to the other side (picking up a minus sign)

10x = -2x + 31 - 7 = -2x + 24

Move -2x to the other side (flipping sign)

12x = 24

Recover 12*2 = 24 via memorization, quick division (though not long division), or whatever method

Therefore, x = 2. Then I drew a square and was done.

>Then I drew a square and was done.

I don't get this part.

You mean to highlight the end result? In that case, it would, most of the time, be a rectangle (or try to be).

I was joking, I meant the QED box.

I know about QED, but I am not familiar with the concept of "QED box".

A cursory web search yielded nothing.

It’s a symbol that goes by many names: the tombstone, end-of-proof, or Q.E.D.

"∎"

Interesting.

I wasn't familiar with this, despite being a graduate. Its use might depend wildly on where.