\[a = 2\frac{2}{3}:\]
\[- 3,8 + a = - 3,8 + 2\frac{2}{3} =\]
\[= - 3\frac{4^{\backslash 3}}{5} + 2\frac{2^{\backslash 5}}{3} =\]
\[= - \left( 3\frac{12}{15} - 2\frac{10}{15} \right) = - 1\frac{2}{15}.\]