What should be taken away from `3x^2-4y^2+5xy+20` to obtain `-x^2-y^2+6xy+20` ?

What should be taken away from 3x^2-4y^2+5xy+20 to get x^2-y^2+6xy+20

An expression is taken away from 3x^(2)-4y^(2)+5xy+20 to obtain -x^(2)-y^(2)+6xy+20, then the expression is.

What should be added to x^(2) - y^(2) +2xy to obtain x^(2) + y^(2) + 5xy ?

What should be added to x^2 + xy + y^2 to obtain 2x^2 + 3xy ?

What should be added to x^(2) +xy + y^(2) to obtain 4x^(2) + 8xy ?

What should be added to x^(2)+xy+y^(2) to obtain 2x^(2)+3xy?

What should be subtracted from 2x^3 - 3x^2y + 2xy^2 + 3y^3 " to get " x^3- 2x^2y + 3xy^2 + 4y^3 ?

What should be added to x^2+xy+y^2 to obtain 2x^2+3xy ?