1. Find the sum of $(4x + 2y - 6z) + (5y - 2z + 7x) + (-9z - 2x - 3y)$. Combine like terms: For $x$: $4x + 7x - 2x = 9x$ For $y$: $2y + 5y - 3y = 4y$ For $z$: $-6z - 2z - 9z = -17z$ So, the sum is $$9x + 4y - 17z$$. 2. Find the sum of $(5a^2 - 4) + (a^2 - 2a + 12) + (4a^2 - 6a + 8)$. Combine like terms: For $a^2$: $5a^2 + a^2 + 4a^2 = 10a^2$ For $a$: $-2a - 6a = -8a$ Constants: $-4 + 12 + 8 = 16$ So, the sum is $$10a^2 - 8a + 16$$. 3. Find the sum/difference of $(3c^2 - 7) + (4c + 7) - (c^2 + 5c - 8)$. Distribute the minus sign to the third expression: $-(c^2 + 5c - 8) = -c^2 - 5c + 8$ Now combine all terms: For $c^2$: $3c^2 - c^2 = 2c^2$ For $c$: $4c - 5c = -c$ Constants: $-7 + 7 + 8 = 8$ So, the result is $$2c^2 - c + 8$$.