Решим уравнения:
$$ z - 6 = 3 : \frac{3}{7} $$
$$ z - 6 = 3 \cdot \frac{7}{3} $$
$$ z - 6 = 7 $$
$$ z = 7 + 6 $$
$$ z = 13 $$
Ответ: 13.
$$ \frac{21}{4} y = \frac{21}{4} + \frac{21}{4} $$
$$ \frac{21}{4} y = \frac{42}{4} $$
$$ y = \frac{42}{4} : \frac{21}{4} $$
$$ y = \frac{42}{4} \cdot \frac{4}{21} $$
$$ y = 2 $$
Ответ: 2.