The answer is 10mm, I answered this in a previous question.
Answer:
C
Step-by-step explanation:
We have:

Where a<0.
We would like to solve for a. So, let’s divide both sides by a.
Notice that a<0. Therefore, a is negative. Hence, we must flip the sign since we are dividing by a negative. This yields:

Now, we will subtract b from both sides. Therefore, our inequality is:

Hence, our answer is C.
For this, all you need to do is subtract 2m on both sides, and your answer will be: -1 = m