1) x + 15 - 8 = 17
x = 17 - 15 + 8 = 10
10 + 15 - 8 = 17
17 = 17
2) 24 + x - 21 = 10
x = 10 + 21 - 24 = 7
24 + 7 - 21 = 10
10 = 10
3) 45 - y + 18 = 58
-y = 58 - 45 - 18
-y = -5
y = 5
45 - 5 + 18 = 58
58 = 58
4) y - 35 + 12 = 32
y = 32 - 12 + 35 = 55
55 - 35 + 12 = 32
32 = 32
5) 56 - x - 12 = 24
-x = 24 + 12 - 56 = - 20
x = 20
56 - 20 - 12 = 24
24 = 24
6) 55 - x + 15 = 30
-x = 30 - 15 - 55 = -40
x = 40
55 - 40 + 15 = 30
30 = 30