Let their ages be 4x and 5x.
Age difference: 5x - 4x = 6 → x = 6.
Younger friend = 4x = 4 × 6 = 24 years.
Thus, the correct answer is: \[ \boxed{\text{24 years}} \]





The Art Institute of Chicago has recreated the famous painting "the bedroom" by Vincent van Gogh.
Carefully observe the image which will disappear after 30 seconds and answer the two following questions. The image cannot be viewed again.
