George sold 18, 22, 26, 12, 25, 20, and 19 cars per month over the past seven months. He followed the steps below to determine the number of cars he needs to sell in the next month to have a mean number of sales per month of 24.

Step 1: Find the total cars needed to have a mean of 24: 24 times 7 = 168.
Step 2: Find the total cars sold: 18 + 22 + 26 + 12 + 25 + 20 + 19 = 142.
Step 3: Subtract the total cars sold from the total cars needed: 168 minus 142 = 26.
Step 4: State the George needs to sell 26 cars next month.

Where did George make his first mistake?