tolong dong aku gak ngerti

6) x2 + 4x +3x +12
= x2 + 7x +12

7) x2 -5x +2x -10
= x2 -3x -10

8)3x2 -15xy +2xy -10y2
= 3x2-13xy -10y2

9) 6x2 +42xy - 8xy -28y2
= 6x2 + 34xy -28y2

10) 20x2 -16xy -15xy + 12y2
= 20x2 -31xy + 21y2