\[\boxed{\mathbf{2.496}}\]
\[\textbf{а)}\ (z - 6) \cdot \frac{3}{7} = 3\]
\[z - 6 = 3\ :\frac{3}{7}\]
\[z - 6 = 3 \cdot \frac{7}{3}\]
\[z = 7 + 6\]
\[z = 13\]
\[Ответ:z = 13.\]
\[\textbf{б)}\ 5\frac{1}{4}y - 5\frac{1}{4} = 5\frac{1}{4}\]
\[5\frac{1}{4}y = 5\frac{1}{4} + 5\frac{1}{4}\]
\[5\frac{1}{4}y = 2 \cdot 5\frac{1}{4}\]
\[y = 2 \cdot 5\frac{1}{4}\ :5\frac{1}{4}\]
\[y = 2.\]
\[Ответ:y = 2.\]