\[\boxed{\mathbf{2.}\mathbf{311}}\]
\[\textbf{а)}\ t - 4\frac{7}{12} = 2\frac{5}{8}\]
\[t = 2\frac{5^{\backslash 3}}{8} + 4\frac{7^{\backslash 2}}{12} =\]
\[= 2\frac{15}{24} + 4\frac{14}{24} = 6\frac{29}{24}\]
\[t = 7\frac{5}{24}.\]
\[\textbf{б)}\ 15\frac{4}{9} - z = 10\frac{5}{12}\]
\[z = 15\frac{4^{\backslash 4}}{9} - 10\frac{5^{\backslash 3}}{12} =\]
\[= 15\frac{16}{36} - 10\frac{15}{36}\]
\[z = 5\frac{1}{36}\text{.\ }\]