Find the sum of (5x3 + 3x2 - 5x + 4) and (8x3 -5x2 + 8x + 9).

If you would like to solve (5 * x^3 + 3 * x^2 - 5 * x + 4) + (8 * x^3 - 5 * x^2 + 8 * x + 9), you can calculate this using the following steps:

(5 * x^3 + 3 * x^2 - 5 * x + 4) + (8 * x^3 - 5 * x^2 + 8 * x + 9) = 5 * x^3 + 8 * x^3 + 3 * x^2 - 5 * x^2 - 5 * x + 8 * x + 4 + 9 = 13 * x^3 - 2 * x^2 + 3 * x + 13

The correct result would be 13 * x^3 - 2 * x^2 + 3 * x + 13.