1) x+(6 2/5-4,91)=5,35
2) y+(9,31-7 1/4)=8,2
3) (7,61-2 3/25)+x=7
4)(8,61-3 3/4)+y=12,1

вам

1) x=5,35-(6,4-4,91)=3,87=3 87/1002) y=8.2-(9,31-7.25)=6.14=6 7/503) х=7-(7,61-2.12)=1,51=1 51/1004) у=12.1-(8,61-3.75)=7.24=7 6/25