15 3/10-2 3/4=12 11/20 ск катера
12 11/20-2 3/4=9 4/5 ск против течения
1.5,6х+9.4х-3,3х=210,6
5,6х+9.4х-3,3х=210,6
11.7х = 210.6
х = 210.6 : 11.7
х = 18
2.16,4х+7.7х-1.9х=555
16,4х+7.7х-1.9х=555
22.2х = 555
х = 555 : 22.2
х = 5550 : 222
х = 25