Answer:
12x + 15 = 12x - 15 can not be solved.
We can not find out what x equals.
Step-by-step explanation:
You can solve - 5x - 25 = 5x + 25
x = - 5
You can solve 7x + 21 = 21
x = 0
You can solve 12x + 15 = 3(4x + 5)
x = AllRealNumbers
That leaves 12x + 15 = 12x - 15
This equation can not be solved
