\[\left\{ \begin{matrix} y = - \frac{3}{8}x + 15 \\ y = \frac{5}{6}x + 73\ \ \ \ \\ \end{matrix} \right.\ \]
\[1)\ - \frac{3}{8}x + 15 = \frac{5}{6}x + 73\]
\[- \frac{3}{8}x - \frac{5}{6}x = 73 - 15\]
\[- \frac{9 + 20}{24}x = 58\ \ \ \ \ \ | \bullet 24\]
\[- 29x = 1392\ \ \ \ |\ :( - 29)\]
\[x = - 48.\]
\[2)\ y = \frac{5}{6} \bullet ( - 48) + 73\]
\[y = - 5 \bullet 8 + 73\]
\[y = 73 - 40\]
\[y = 33.\]
\[3)\ y + px = 0\]
\[33 + p \bullet ( - 48) = 0\]
\[48p = 33\]
\[p = \frac{33}{48}\]
\[p = \frac{11}{16}.\]
\[Ответ:\ \ при\ p = \frac{11}{16}.\]