He/she got the number sentence (17 + 25 = 42 - with the square around the 42).
Why a box? Why not just teach the students to write neatly and put the answer after the equals sign?
(I know why--it is to make the teacher's job easier grading papers, so they only have to look for the box.)
"Number sentences" used to be known (and still are) as "equations". It seems simpler to me to just call an equation an equation, but then, I have noticed subtle changes in the accepted terminology and methodology which not only make the next edition of the text different from the previous one, but make the parents look dumb.
Making the parents look dumb seems to be the goal, so that later on in life when they tell their children about things like the Bill of Rights, try to set them straight on the History of those mean old whitemen who owned slaves (guys like Washington and Jefferson and Madison) the kids will already have it planted that their parents don't know anything and the teacher has it right.
Arithmetic isn't hard unless you make it more confusing than it needs to be. I should be able to pull out the primary level arithmetic books I have from the 1930s and earlier, and get the same answer to the same problem, but when the focus is on the methodology rather than the correct answer, and the methodology changes, the result is to make it appear that older folks don't know what they are doing.
Whether that truly has a seditious component or it is to make the latest text appear more relevant to sell books (or a combination), the result is unnecessary confusion.
YMMV.