Final answer:
To cut a client's hair to the length it was 6 months ago, you would typically remove 3 inches, assuming an average monthly hair growth rate of half an inch. This figure is based on average growth, and individual rates may vary.
Step-by-step explanation:
To determine how many inches of hair should be removed after 6 months to achieve the same length as in January, one must know the average monthly hair growth rate. On average, hair grows about half an inch per month. Therefore, over 6 months, a person's hair could grow approximately 3 inches.
To return the client's hair to the length it was in January, you would need to cut off the growth that occurred in those 6 months. Assuming an average growth and that no haircuts were given during that period, you would remove 3 inches of hair to achieve the same length as in January.
Note that this is based on average hair growth and individual growth rates can vary. Any haircuts or trims the client had during those 6 months would also affect how much you need to remove. If the client's hair growth rate is significantly different from the average, adjust the amount accordingly.