You have the following expression:
(7x³ - 5x² + 10) + (x³ + 8x² - 5x)
In order to simplify the previous expression, first eliminate parenthesis:
7x³ - 5x² + 10 + x³ + 8x² - 5x order terms
= 7x³ + x³ - 5x² + 8x² - 5x + 10 simplify like terms
= 8x³ + 3x² - 5x + 10
Hence, the simplified expression is:
8x³ + 3x² - 5x + 10