Identify the error and fix the mistake

Answer:
x = (9 ±√201) ÷ 12
Step-by-step explanation:
6x² -5x -9 = 0 ( rearranged)
a = 6 b = -5 c = -9
- - 9 = 9
-9² = 81 (the 81 must be positive, this is one error)
-4 x 6 x -5 = 120 ( the 5 must be a minus number, this is one error)
120 + 81 = 201
x = (9 ±√201) ÷ 12