\(3x=10y\Leftrightarrow\frac{x}{y}=\frac{10}{3}\)

A=\(\frac{16x^2-40xy}{8x^2-24xy}=\frac{\frac{16x^2}{8xy}-\frac{40xy}{8xy}}{\frac{8x^2}{8xy}-\frac{24xy}{8xy}}=\frac{2\frac{x}{y}-5}{\frac{x}{y}-3}=\frac{2.\frac{10}{3}-5}{\frac{10}{3}-3}=\frac{\frac{5}{3}}{\frac{1}{3}}=5\)