[tex]\displaystyle\bf\\ \frac{x}{y}=\frac{2}{5}\\\\x=\frac{2y}{5}\\\\\frac{10x-14y+8}{5x+3y-4}=\\\\\\=\frac{10\cdot\dfrac{2y}{5}-14y+8}{5\cdot\dfrac{2y}{5}+3y-4}=\\\\\\=\frac{4y-14y+8}{2y+3y-4}=\\\\\\=\frac{-10y+8}{5y-4}=\\\\\\=\frac{-2(5y-4)}{5y-4}=-2\cdot\frac{5y-4}{5y-4}=-2\cdot1=\boxed{\bf-2}[/tex]
