Answer :

[tex]\frac{3}{5}=\frac{x}{x+2y}\ \ \ \ \ |cross\ multiply\\\\3(x+2y)=5(x)\\3(x)+3(2y)=5x\\3x+6y=5x\ \ \ \ \ |subtract\ 3x\ from\ both\ sides\\6y=2x\\2x=6y\ \ \ |divide\ both\ sides\ by\ 2\\x=3y\ \ \ \ |divide\ both\ sides\ by\ y\\\boxed{\frac{x}{y}=3}[/tex]
3/5=x/(x+2y)
multiply both side by x+2y
x=3/5 x (x+2y)
x=3x/5 + 6y/5
x=(3x+6y)/5
multiply both side by 5
5x=3x+6y
subtract both side by 3x
2x=6y
simplify both side by 2
x=3y
divide both side by y
x/y=3