<s>[INST] Working Out Easy Equations does anyone know how to do this equation? I know it's easy but I can't work out what the question means.

When I expanded the first equation:
$(y+4)-(y-3)$
$y^2 -3y +4y - 12$
$y^2-1y-12$
Not sure what I should do after.
Can someone explain how would you work it out in easy terms?
Thank you
 [/INST] $$(y + 4) - (y - 3) = (y + 4) - (y) - (-3) = (y+4) + (3 - y) = (y - y) + (3 + 4) = 7$$
$$(y-2) - (y - 3) = (y - 2) - y - (-3) = (y-2) + (3 - y) = (y - y) + (3 - 2) = 1$$
In general,
$$(y-a) - (y - b) = b - a$$
In the same way that $x + (y + z) = x + y + z$, $x - (y + z) = x - y - z$. The minus sign distributes to all terms and reverses their sign. Mainly because 
$$z - (x + y) = z + (-1)(x + y) = z + (-1)x + (-1)y = z - x - y$$
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