you can only add like terms
exg
you can addd
2+4
2x+4x
2x^2+4x^2
2x^3+4x^3
but not
2+4x
2x^2+2x^3
so when adding like terms keep the exponent
4x+2x=6x
4x^3+2x^3=6x^3
(7x^2+4x-7)+(4x^2-6x+4)
get rid of the parenthasees
7x^2+4x-7+4x^2-6x+4
group like terms (x^2 with x^2 x with x, etc)
(7x^2+4x^2)+(4x-6x)+(-7+4)
add like terms
11x^2-2x-3