The proportion of clay uses is 3/8 (Three Eighths). That is 3 lbs. of clay to every 8 vases. This is determined by the first given proportion 3 lbs./8 vases and confirmed by the second. To prove that is the case you divide the second ration by the first numerator: 9 divided by 3 = 3 and 24 divided by 3 = 8. So the proportion for 9/24 is still 3/8. This can also be used to increase the number of vases made. For example if 40 vases need to be made: we divide 40 by the numerator 8 = 5. So we need 5 portions of 3 to make 40 vases. 5 times 3 = 15. So the 15 lbs. of clay is needed for 40 vases.