Теңдеуді шешіңдер
(12/5/13+y)-9/9/13=7/7/13​

(12 5/13 + y) - 9 9/13) = 7 7/13          

12 5/13 + у - 9 9/13 = 7 7/13

у = 7 7/13 + 9 9/13 - 12 5/13

у = 16 16/13 - 12 5/13

у = 4 11/13

Проверка:

(12 5/13 + 4 11/13) - 9 9/13) = 16 16/13 - 9 9/13 = 7 7/13

(12 5\13+у)-9 9\13=7 7\13

12 5/13+y=7 7/13+9 9/13

12 5/13+y=17 3/13

y=17 3/13-12 5/13

y=4 11/13