Answer:
C) Step 3
Explanation:
We are given that

We have to find the mistake made by Mia in her solution.
Step 1:

Reason: Given
Step 2:


Reason: Subtraction property of inequality
Step 3:


Reason: Using subtraction property of inequality
Step 4:


Reason: Division property of inequality
Mia did mistake in step 3 .She using addition property instead of subtraction property.
Option C is true.