\[3\frac{5}{12} - \left( - 1\frac{1}{3} \right) + \left( - 4\frac{3}{8} \right) =\]
\[= 3\frac{5 \cdot 2}{24} + 1\frac{1 \cdot 8}{24} - 4\frac{3 \cdot 3}{24} =\]
\[= 3\frac{10}{24} + 1\frac{8}{24} - 4\frac{9}{24} =\]
\[= 4\frac{18}{24} - 4\frac{9}{24} = \frac{9}{24} = \frac{3}{8}\text{.\ }\]