Answer: He made a mistake on Step 3
Step-by-step explanation: He made a mistake on Step 3, he did not add and subtract correctly, [$171 + $52.45 − $18.50} is not equal to $241.95. It is actually 204.95. He can correct his error by trying to re-do his equation and see if he gets the same answer.
(I hope that was correct!) :3