Помагите найти ооф..........

Решите задачу:

$a)\; OOF:\; \left \{ {{5x+4\ \textgreater \ 0} \atop {8x+7\ \textgreater \ 0}} \right. \; \left \{ {{x\ \textgreater \ -\frac{4}{5}} \atop {x\ \textgreater \ -\frac{7}{8}}} \right. \; \; \to \; \; x\ \textgreater \ -\frac{4}{5}\\\\b)\; OOF:\; \left \{ {{6x+5\ \textgreater \ 0} \atop {7+8x\ \textgreater \ 0}} \right. \; \left \{ {{x\ \textgreater \ -\frac{5}{6}} \atop {x\ \textgreater \ -\frac{7}{8}}} \right. \; \; \to \; \; x\ \textgreater \ -\frac{5}{6}$