Final answer:
The solution set of the given equation is ∅ (empty set).
Step-by-step explanation:
To find the solution set of the equation -5x + x + 9 = -4x + 12, we need to simplify the equation and isolate x.
-5x + x + 9 = -4x + 12
-4x + 9 = -4x + 12
When we subtract -4x from both sides of the equation, we get:
9 = 12
Since 9 is not equal to 12, there is no solution to this equation. Therefore, the solution set is ∅ (empty set), which makes option b) the correct answer.