\[\boxed{\mathbf{617\ (617)}\mathbf{.}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
Пояснение.
Решение.
\[1)\frac{b}{a} = \frac{3}{7}\]
\[3 \cdot a = 7 \cdot b\]
\[\frac{a}{b} = \frac{7}{3} = 2\frac{1}{3}.\]
\[2)\frac{16}{b} = \frac{9}{a}\]
\[16 \cdot a = 9 \cdot b\]
\[\frac{a}{b} = \frac{9}{16}.\]