book Maths Puzzle Numerical Ability

i do not understand polynomials AT ALL so any help would greatly be appreciated
(2x squared +3x - 5)+ (7x squared -x+7)=
i tried it and this is what i got for the answer
9xsquar

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book Other Question
the some of 20 and a number is 30 how do you simplify this expression?
(3x^2+2y^2+4x+8y)+(x^2-y^2)