1.a. 3x + 8 + 7x + 7
= 10x + 15

b.3x-2y + 3z +2a^2 -5y + 6z
= 3x + 2a^2 -7y + 9z

c.6x^2+4x-21+3x^2-14x+7
= 9x^2 -10x -14

d.2(4a+7b+3) + 5(2b-3a+2)
=8a+14b + 6 + 10b -15a + 10
=-7a + 24b + 16

e.(-x^2-3x+5)+3(4x^2 +2x-5)
=-x^2 -3x + 5 + 12x^2 + 6x -15
= 11x^2 + 3x -10