989,6: (20,73-2,09*х)-12,45=67,55 от этого

989,6/(20,73 - 2,09х) - 12,45 = 67,55
989,6/(20,73 - 2,09х) = 80
20,73 - 2,09х = 989,6/80
20,73 - 2,09х = 12,37
2,09х = 20,73 - 12,37
2,09х = 8,36
х = 8,36/2,09
х = 836/209
х = 4

ОТВЕТ: 4