111-3(x-3(x-3(x-3)))=3

111-3(х-3(х-3(х-3)))=3,
111-3(х+6х-27)=3,
111-3(7х-27)=3,
111-21х+81=3,
192-21х=3,
-21х=3-192,
-21х=-189,
х=9.
Ответ: 9.