To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $y$ and $5x$ is $5xy$. Multiply $\frac{5x}{y}$ times $\frac{5x}{5x}$. Multiply $\frac{y}{5x}$ times $\frac{y}{y}$.
$$\frac{5x\times 5x}{5xy}-\frac{yy}{5xy}$$
Since $\frac{5x\times 5x}{5xy}$ and $\frac{yy}{5xy}$ have the same denominator, subtract them by subtracting their numerators.
