How would one simplify this type of equation

[-3x^(2) + 7x +23]+[-8x^(2) - 5x +13]
as well as the same thing but middle sign reversed:
[-3x^(2) + 7x +23]-[-8x^(2) - 5x +13]

I know the answers are:
-3x^2-8x^2+7x-5x+23+13
=
-11x^2+2x+36
and
-3x^2+8x^2+7x+5x+23-13
=
5x^2+12x+10
but how do you come to these solutions

YOU JUST HAVE TO LINE everything up!

so -3x^2+7x+23+ -8x^2-5x+13
-3x^2-8x^2+7x-5x+23+13
-11x^2+2x+36

the only thing you have to watch out for is that +(-8x^2), which is converted to a -8x^2