9. Subtract

(x2 + 7x - 8) - (2x2 - 4x + 5)

The second polynomial is being subtracted, so when we remove parentheses, we need to change the signs on all the terms inside.

x2 + 7x - 8 - 2x2 + 4x - 5

Now combine like terms

-x2 + 11x - 13

When we use the vertical format, we simply change the sign on the terms in the polynomial we are subtracting when we write it underneath the other polynomial.