Answer:
Step 3
Step-by-step explanation:
Here, the given expression,

Since, when we solve the given expression the steps of solution are as follows,
Step 1 : 7b + 3.2b - 5 = 18.92
Step 2 : 10.2b - 5 = 18.92 ( Combining like terms in left side )
Step 3 : 10.2b = 23.92 ( Adding 5 on both sides )
Step 4 : b = 4.6 ( Dividing both sides by 10.2 )
Hence, by the above explanation it is clear that she made her mistake in step 3 ( she did not add 5 on right side )