х+2х=21.42...................................
х+2х=21.42...
3==21,42
х=21,42/3
х=7, 14
проверка
7,14+2*7,14=21,72
7,14+14,28=21,72
21,72=21,72
х+2х=21.42
3х=21,42
х=21,42:3
х=7,14