(853-x):19-16=20
(853-x):19 =16+20
(853-x):19 = 36
853 - x = 36 * 19
853 - x = 684
x = 853-684
x = 169
проверка
(853-169) : 19 - 16 = 20
684 : 19 - 16 = 20
36 - 16 = 20
20 = 20
165+(7x-8)=255
7х - 8 = 255 - 165
7х - 8 = 90
7х= 8 + 90
7х=98
х=98 :7
х=14
проверка
165 + (7 * 14 - 8) = 255
165 + (98 - 8) = 255
165 + 90 = 255
255 = 255