[tex] \frac{x}{y} = \frac{1}{3} = > x = \frac{y}{3} [/tex]
[tex] \frac{4x - y}{x + y} = \frac{ \frac{4y}{3} - y}{ \frac{y}{3} + y} = \frac{ \frac{4y - 3y}{3} }{ \frac{y + 3y}{3} } = \frac{ \frac{y}{3} }{ \frac{4y}{3} } = \frac{y}{4y} = \frac{1}{4} [/tex]