If x is subtracted from each of 24, 40, 33 and 57, the numbers, so obtained are in proportion. The ratio of (5x + 12) to (4x + 15) is:

14 : 13

The proportion of these numbers, 

(24 - x) : (40 - x)  :: (33 - x) : (57 - x) 

The product of middle terms = product of extreme terms 

(40 - x)(33 - x) = (24 - x)(57 - x)

1320 - 40x - 33x + x² = 1368 - 24x - 57x + x² 

8x = 48 or x = 6

Thus, (5x + 12) : (4x + 15)

(5 x 6 + 12) : (4 x 6 + 15) 

42 : 36 = 14 : 13