[tex]\frac{a}{b}=\frac{3}{5} \\ \\ a=\frac{3b}{5}[/tex]
Inlocuim pe a cu 3b/5
[tex]\frac{a+b}{3a-b}=\frac{\frac{3b}{5}+b}{3\cdot\frac{3b}{5}-b} \\ \\ =\frac{\frac{3b}{5}+\frac{5b}{5}}{\frac{9b}{5}-\frac{5b}{5}} \\ \\ =\frac{\frac{8b}{5}}{\frac{4b}{5}} \\ \\ =\frac{8b}{4b}=\frac{8}{4}=2[/tex]
