\[\boxed{\mathbf{2.}\mathbf{207}}\]
\[\textbf{а)}\ 99\frac{15}{5} = 99 + \frac{15}{5} = 99 + 3 =\]
\[= 102\]
\[\ \ 207\frac{101}{101} = 207 + \frac{101}{101} =\]
\[= 207 + 1 = 208\]
\[\textbf{б)}\ 8\frac{17}{4} = 8 + \frac{17}{4} = 8 + 4\frac{1}{4} =\]
\[= 12\frac{1}{4}\]
\[16\frac{25}{9} = 16 + \frac{25}{9} = 16 + 2\frac{7}{9} =\]
\[= 18\frac{7}{9}\]
\[31\frac{107}{4} = 31 + \frac{107}{4} =\]
\[= 31 + 26\frac{3}{4} = 57\frac{3}{4}\]