\[\boxed{\mathbf{3.}\mathbf{292}}\]
\[\textbf{а)}\ 77\ 770\ :110 + x = 708\]
\[707 + x = 708\]
\[x = 708 - 707\]
\[x = 1.\]
\[\textbf{б)}\ 7761 + p\ :123 = 8000\]
\[p\ :123 = 8000 - 7761\]
\[p\ :123 = 239\]
\[p = 239 \cdot 123\]
\[p = 29\ 397.\]
\[\textbf{в)}\ 2730 + 1216\ :y = 2794\]
\[1216\ :y = 2794 - 2730\]
\[1216\ :y = 64\]
\[y = 1216\ :64\]
\[y = 19.\]
\[\textbf{г)}\ 13\ 755\ :131 + k = 105\]
\[105 + k = 105\ \]
\[k = 105 - 105\]
\[k = 0.\]