Answer:
Step-by-step explanation:
The error is in the second step. For some unknown reason, the x was dropped and the 3 was subtracted from the 7.
It should be
9x +3x + 12 = 7
12x + 12 = 7 Subtract 12 from both sides.
12x + 12 - 12 = 7 - 12 Combine
12x = -5 Divide by 12
12x/12 = -5/12
x = -5/12 or x = - 0.4167
