Respuesta :

(10x - 4xsquare) - (7x+?)=3x- 6x square
so
 ( 10x - 4x^2) - (7x + 2x^2) 
= 10x - 4x^2 -7x - 2x^2 
=  3x - 6x^2 

answer
missing term is (-2x^2)