<h2>Hello!</h2>
The answer is: George made his first mistake in Step 1.
<h2>Why?</h2>Getting a result of 26 cars needed means that he didn't take in consideration the next month in the mean calculation.
We have information of the number of sold cars of the first seven months, but if he wants to calculate the number of cards he needs to have a mean of 24 sold cards next months, he should take in consideration an extra month (the eighth month).
Checking the mistake:
So, it proves that he made a mistake by multiplying it into 7 and instead into 8
The correct answer would be:
He needed to include the eighth month in order to calculate how many cars he should sell next months in order to have a mean of 24 cars.
Have a nice day!