\[\boxed{\mathbf{4.}\mathbf{39}}\]
\[\textbf{а)} - ( - 21) = + 21\]
\[\textbf{б)}\ 4,7 = - ( - 4,7)\]
\[\textbf{в)} - ( - 13,2) = + 13,2\]
\[\textbf{в)}\ 49 = - ( - 49)\]
\[\textbf{г)} - \left( - \frac{9}{19} \right) = + \frac{9}{19}\]
\[\textbf{д)}\ 16\frac{7}{13} = + 16\frac{7}{13}\]