первый:
(х-2 1/3) + 3 7/9 = 14 4/9
(х-7/3)+34/9 = 130/9
х-7/3+34/9=130/9
х+13/9=130/9
х=130/9-13/9
х=13
второй:
(8 4/21 + у) - 7 13/21 =12 4/7
(172/21 + у) -160/21 = 88/7
172/21+у - 160/21=88/7
4/7+у=88/7
у= 88/7+4/7
у=12
