P = -4b^2 + 6b - 9
Q = 7b^2 - 2b - 5
P - Q = ?
Combine like terms (which involve b^2, b and constants):
P - Q = -4b^2 - 7b^2 + 6b - (-2b) - 9 - (-5), or:
P - Q = -11 b^2 + 8b - 4
