\[\boxed{\text{4.\ 223}}\]
\[x + y\]
\[\textbf{а)}\ x = - 1,7;y = 3,4:\]
\[x + y = - 1,7 + 3,4 = 1,7.\]
\[\textbf{б)}\ x = - 11,3;y = 10,8\]
\[x + y = - 11,3 + 10,8 =\]
\[= - (11,3 - 10,8) = - 0,5.\]
\[\textbf{в)}\ x = - \frac{4}{9};\ \ y = \frac{2}{3}:\]
\[x + y = - \frac{4}{9} + \frac{2}{3} = \frac{6}{9} - \frac{4}{9} = \frac{2}{9}.\]
\[\textbf{г)}\ x = \frac{7}{24};\ \ y = \frac{7}{16}:\]
\[x + y = \frac{7}{24} + \frac{7}{16} = \frac{14}{48} + \frac{21}{48} =\]
\[= \frac{35}{48}.\]