\(\frac{3x-y}{x+y}=\frac{3}{4}\\ \Rightarrow3\left(x+y\right)=4\left(3x-y\right)\\ \Rightarrow3x+3y=12x-4y\\ \Rightarrow12x-3x=4y+3y\\ \Rightarrow9x=7y\\ \Rightarrow\frac{x}{y}=\frac{7}{9}\)
\(\frac{3x-y}{x+y}=\frac{3}{4}\)
\(\Rightarrow\left(3x-y\right).4=\left(x+y\right).3\)
\(\Rightarrow12x-4y=3x+3y\)
\(\Rightarrow12x-3x=3y+4y\)
\(\Rightarrow9x=7y\)
\(\Rightarrow\frac{x}{y}=\frac{7}{9}\)
Vậy \(\frac{x}{y}=\frac{7}{9}.\)
Chúc bạn học tốt!