Express in simplest form with a rational denominator. \[ \frac{3}{\sqrt{28}} \]

To simplify the expression \(\frac{3}{\sqrt{28}}\), first, we simplify the square root in the denominator. The number 28 can be factored as \(4 \times 7\), and since \(\sqrt{4} = 2\), we have: \[ \sqrt{28} = \sqrt{4 \times 7} = \sqrt{4} \cdot \sqrt{7} = 2\sqrt{7} \] Now substituting this back into the fraction gives us: \[ \frac{3}{\sqrt{28}} = \frac{3}{2\sqrt{7}} \] To rationalize the denominator, multiply the numerator and denominator by \(\sqrt{7}\): \[ \frac{3}{2\sqrt{7}} \cdot \frac{\sqrt{7}}{\sqrt{7}} = \frac{3\sqrt{7}}{2 \cdot 7} = \frac{3\sqrt{7}}{14} \] So the simplified form of \(\frac{3}{\sqrt{28}}\) with a rational denominator is: \[ \frac{3\sqrt{7}}{14} \]