Answer:
x³ - 3x² + 12
Explanation:
Let N be the unknown addend.
4x³ + x² + 5 = 3x³ + 4x² - 7 + N
Combine like/similar terms.
4x³ + x² + 5 - 3x³ - 4x² + 7 = N
x³ - 3x² + 12 = N
Checking:
4x³ + x² + 5 = 3x³ + 4x² - 7 + x³ - 3x² + 12
4x³ + x² + 5 = 4x³ + x² + 5