tolong jawabnya pake cara

no 6
15x²-3xy+6y²-18x²+5xy+2y²
=(15x²-18x²)+(-3xy+5xy)+(6y²-2y²)
=3x²+2xy+4y²
jadi jawabannya d

6. 15x2 - 3xy + 6y2 - 18x2 + 5xy + 2y2 = -3x2 + 2xy + 8y2
7. 2(3x2-2x+5) + 3(6x2 + 2x -7 ) = 6x2 - 4x +10 + 18x2 + 6x - 21 = 24x2 + 2x - 11
8. -7 ( 3y2+ 2y -7 ) - -6(5x +4y -13) = -21y2 -14y + 49 + 30x + 24y + 13 = -21y2  + 10y + 30x + 62