$$ (x + 15) - 8 = 17 $$
$$ x + 15 = 17 + 8 $$
$$ x + 15 = 25 $$
$$ x = 25 - 15 $$
$$ x = 10 $$
Ответ: x = 10
$$ (24 + x) - 21 = 10 $$
$$ 24 + x = 10 + 21 $$
$$ 24 + x = 31 $$
$$ x = 31 - 24 $$
$$ x = 7 $$
Ответ: x = 7
$$ (45 - y) + 18 = 58 $$
$$ 45 - y = 58 - 18 $$
$$ 45 - y = 40 $$
$$ -y = 40 - 45 $$
$$ -y = -5 $$
$$ y = 5 $$
Ответ: y = 5
$$ (y - 35) + 12 = 32 $$
$$ y - 35 = 32 - 12 $$
$$ y - 35 = 20 $$
$$ y = 20 + 35 $$
$$ y = 55 $$
Ответ: y = 55