Ratios, rates, proportional relationships, and units SAT question

The correct answer is $24$. The equation $\frac{24x}{ny}=4$ can be rewritten as $(\frac{24}{n})(\frac{x}{y})=4$. It's given that $\frac{x}{y}=4$. Substituting $4$ for $\frac{x}{y}$ in the equation $(\frac{24}{n})(\frac{x}{y})=4$ yields $(\frac{24}{n})(4)=4$. Multiplying both sides of this equation by $n$ yields $(24)(4)=4n$. Dividing both sides of this equation by $4$ yields $24=n$. Therefore, the value of $n$ is $24$.