(28/42-а)-13/42=11/42

Question

(28/42-а)-13/42=11/42

Answer 1

28/42 - а - 13/42 = 11/42
15/42 - а = 11/42
 а = 15/42 - 11/42
 а = 4/42
 а = 2/21

Answer 2

(28/42-а)-13/42=11/42
28/42-а-13/42=11/42
-а=11/42+13/42-28/42
-а=-4/42
а=2/21