Division involving a whole number and a fraction Divide. Write your answer in simplest form. \[ 9 \div \frac{4}{9} \]

Step 1 ：To divide by a fraction, we multiply by its reciprocal. The reciprocal of \(\frac{4}{9}\) is \(\frac{9}{4}\).

Step 2 ：Therefore, the problem becomes: \(9 \times \frac{9}{4}\).

Step 3 ：To multiply fractions, we multiply the numerators together and the denominators together. In this case, the denominator is 4, which is a whole number, so we can simply multiply 9 by 9 and then divide by 4.

Step 4 ：So, the calculation is: \(\frac{9 \times 9}{4} = \frac{81}{4}\).

Step 5 ：\(\boxed{20 \frac{1}{4}}\) is the final answer in simplest form.