Answer:
The slope is -3.
Explanation:
We can use the formula y= mx+b to answer this question. In this case the slope is m. In the equation C = -3t + 12, m = -3, so the slope is -3. You can tell that this is the slope because it is the number in front of the variable (t). I don't know the context of the problem, so unfortunately I cannot help you with that part of the problem.