Find $\frac{y}{x}$ from $3x + 3y = yt = xt + 2.5x$ I need to find the ratio of
 $$\frac{y}{x}$$
If given that
$$3x + 3y = yt = xt + 2.5x$$
So what I tried is:
$$t = \frac{3x + 3y}{y}$$
And then put it in the equation
$$\frac{x(3x + 3y)}{y} + 2.5x = \frac{(3x + 3y)}{y}y$$
$$\frac{x(3x + 3y)}{y} + 2.5x = 3x + 3y$$
$$\frac{3x^2}{y} + \frac{3yx}{y} + 2.5x = 3x + 3y$$
$$\frac{3x^2}{y} + 3x + 2.5x = 3x + 3y$$
$$\frac{3x^2}{y} + 2.5x = 3y$$
Here I got stuck. I didn't know how to find the ratio. Can someone help me?

Assuming your calculations so far are correct (I didn't check), you are almost there. Divide both sides by $y$, you will get
$$\frac {3x^2} {y^2} + \frac {2.5x} y = 3,$$
a quadratic equation for $\frac xy$.
