3. (2x2 - 3x + 5) + (x2 + 4x - 6)

This is an addition of polynomials problem. Therules for adding polynomials is "Remove parentheses and combine like terms."

Remove parentheses

2x2 - 3x + 5 + x2 + 4x - 6

If there is nothing in front of the parentheses except maybe a plus sign, then nothing happens when you remove them. Now combine like terms.

2x2 + x2 - 3x + 4x + 5 - 6

3x2 + x - 1