1)(5x^2+8x-7)-(2x^2-2x-12)= 5x^2+8x-7- 2x^2+2x+12 = 3x^2 + 10x + 5
2)(2x-3)+(-2x^2-5x-18)= 2x-3 -2x^2-5x-18 = -2x^2 - 3x - 18
3)(6a^2-3a+11)-(-3a-a^2+7)= 6a^2-3a+11 +3a +a^2-7 =7a^2 +6
4)(14ab-9a^2-3b^2)-(-3a^2+5ab-4b^2)= 14ab-9a^2-3b^2 + 3a^2-5ab+4b^2= -6a^2+ b^2 + 9ab
5)(7xy^2-15xy+3x^2y)+(30xy-8x^2y)= 7xy^2-15xy+3x^2y +30xy-8x^2y = 7xy^2-5x^2y +15xy