\[3\frac{1}{6} + \left( - 2\frac{5}{9} \right) - \left( - 1\frac{7}{12} \right) =\]
\[= 3\frac{2}{12} + 1\frac{7}{12} - 2\frac{5}{9} = 4\frac{9}{12} - 2\frac{5}{9} =\]
\[= 4\frac{3}{4} - 2\frac{5}{9} = 4\frac{27}{36} - 2\frac{20}{36} = 2\frac{7}{36}\]