To prove that the product of \( \sqrt{36} \) and \( \frac{5}{3} \) is a rational number, we first calculate the product.
\[ \sqrt{36} = 6 \]
Now, we find the product:
\[ 6 \times \frac{5}{3} = \frac{6 \times 5}{3} = \frac{30}{3} = 10 \]
Since \( 10 \) is a whole number, it is also a rational number (all integers are rational as they can be expressed as a fraction with a denominator of 1). Thus, the product of \( \sqrt{36} \) and \( \frac{5}{3} \) is a rational number.