[tex] \frac{x}{y} = 0.6 = \frac{6}{10} = \frac{3}{5} [/tex]
[tex] \frac{x}{y} = \frac{3}{5} = > 5x = 3y = > x = \frac{3y}{5} [/tex]
[tex] \frac{x + y}{3x + y} = \frac{ \frac{3y}{5} + y}{3 \times \frac{3y}{5} + y } = \frac{ \frac{3y}{5} + \frac{5y}{5} }{ \frac{9y}{5} + \frac{5y}{5} } = \frac{ \frac{3y + 5y}{5} }{ \frac{9y + 5y}{5} } [/tex]
[tex] = \frac{ \frac{8y}{5} }{ \frac{14y}{5} } = \frac{8y}{5} \times \frac{5}{14y} = \frac{8y}{14y} = \frac{4}{7} [/tex]
