(7у-3у):8-9=8;
4y : 8 = 8 + 9
4y : 8 = 17
4y = 17 * 8
4y = 136
y = 136 : 4
y = 34
(6х+х):13+21=35;
7x : 13 = 35 - 21
7x : 13 = 14
7x = 14 * 13
7x = 182
x = 182 : 7
x = 26
48:(9х-х)+25=27
48 : 8x = 27 - 25
48 : 8x = 2
8x = 48 : 2
8x = 24
x = 24 : 8
x = 3