I don't think it is. From my own recollection the usual notation would be more like:

4+3+2 = ? + 2 or 4+3+2 = _ + 2

Along with instructions asking something like "What number would make this true?" And usually it wouldn't be so trivial (though still not difficult, except perhaps at the time):

4+3+2 = _ - 8

Maybe it's just Texas?

Not sure why they used parentheses rather than a letter variable in the example. Having gone through the American education system myself, I can definitely tell you 4+3+2=x+2 is a much more common syntax.