\(\Leftrightarrow\frac{x}{8}=\frac{y}{12}=\frac{z}{15}=\frac{x-y-z}{8-12-15}=\frac{28}{-19}\)
\(\Leftrightarrow x=-\frac{8.28}{19}=-\frac{224}{19}\)
\(\Leftrightarrow y=-\frac{12.28}{19}=-\frac{336}{19}\)
\(\Leftrightarrow z=-\frac{15.28}{19}=-\frac{420}{19}\)