Ta có :\(\frac{2x-3y}{5}=\frac{5y-2z}{3}=\frac{3z-5x}{2}\)
=> \(\frac{10x-15y}{25}=\frac{15y-6z}{9}=\frac{6z-10x}{4}=\frac{10x-15y+15y-6z+6z-10x}{25+9+4}=\frac{0}{38}=0\)
=> \(\hept{\begin{cases}2x=3y\\5y=2z\\3z=5x\end{cases}}\Leftrightarrow\frac{x}{3}=\frac{y}{2}=\frac{z}{5}\)
Đặt \(\frac{x}{3}=\frac{y}{2}=\frac{z}{5}=k\Leftrightarrow\hept{\begin{cases}x=3k\\y=2k\\z=5k\end{cases}}\)
Khi đó B = \(\frac{12x+5y-3z}{x-3y+2z}=\frac{36k+10k-15k}{3k-6k+10k}=\frac{31k}{7k}=\frac{31}{7}\)