8 1/12 + x + x + 11 3/8=39 5/24
97 /12 + 2х + 91/8 = 941 /24
2х = 941/24 - 97/12 -91/8
2х = 941/24 -194/24 - 273/24
2х = 474/24 = 79/4
х = 79/8 = 9 7/8
проверка
97/12 + 79/8 + 79/8 +91/8 = 941/24
97/12 +249/8 = 941/24
194/24+ 747/24 = 941/24
941/24 = 941/24