Question:
Brianna solved a two-step equation, but she made a mistake along the way.

Line 1
: 
Line 2
: 
Line 3
: 
Line 4: 
Answer:
On Line 3, Brianna should have divided by 0.1 instead of subtracting 0.1.
Step-by-step explanation:
Required
Where did she make a mistake?
To do this, we simply analyse her workings one step at a time
Equation: 
Line 1
: 
This is correct because she subtracted 0.3 from both sides
Line 2
: 
This is also correct because she performed the arithmetic correctly
Line 3
: 
This is incorrect.
Division by 0.1 is expected not subtraction