Subtract: (6x² + 3x + 4) - (-5x³ + 2x² - 9)
What would be the next step in solving this problem?

a. (6x² + 5x³) + (3x + 2x²) + (4 - 9)
b. (6x² + 2x²) + (3x - 5x³) +(4 + 9)
c. (6x² + 2x²) + (4-9) + 3x - 5x³
d. (6x² + 3x + 4) + (5x³ - 2x² + 9)