2/3х+1/4х+17/12=5 1/12
11/12х+17/12=61/12
11/12х=61/12-17/12
11/12х=44/12
11/12х=4
х=4/(11/12)
х= 4*12/11
х=4
проверка:
(11/12)*4 +17/12=5 1/12
4+17/12=5 1/12
5 1/12=5 1/12