\[- 13,24 + b + 4,9 + 8,24 + ( - 4,9) =\]
\[= - (13,24 - 8,24) + (4,9 - 4,9) + b =\]
\[= - 5 + b\ \]
\[при\ b = 3\frac{4}{9}:\]
\[- 5 + b = - 5 + 3\frac{4}{9} = - 1\frac{5}{9}\text{.\ }\]