Add:

(2/3x^2-4x-1)+(1/3x^2-19x+28)

Simplify as much as possible.

(2/3x^2-4x-1)+(1/3x^2-19x+28)

= (2/3)x^2 + (1/3)x^2 - 4x - 19x - 1 + 28
= x^2 -23x + 27