
Setting $x = 3$ and $y = 15,$ we get
\[3f(15) = 15f(3).\]Since $f(15) = 20,$ this reduces to $60 = 15f(3),$ so $f(3) = \boxed{4}.$

The answer is: 4
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
The function $f(x)$ satisfies
\[xf(y) = yf(x)\]for all real numbers $x$ and $y.$  If $f(15) = 20,$ find $f(3).$

### Answer:
