The expression \( 3\sqrt{5} \) can be expressed using rational exponents. The cube root can be represented as an exponent of \( \frac{1}{3} \). Therefore, \( 3\sqrt{5} \) can be rewritten as:
\[ 5^{\frac{1}{3}} \]
Here, the rational exponent for the expression equivalent to \( 3\sqrt{5} \) is \( \frac{1}{3} \).