4/9*81/4

To simplify the expression \( \frac{4}{9} \times \frac{81}{4} \), you can multiply the numerators and the denominators:

\[ \frac{4 \times 81}{9 \times 4} \]

Now, you can see that the \(4\) in the numerator and the \(4\) in the denominator can be canceled out:

\[ \frac{81}{9} \]

Next, simplify \( \frac{81}{9} \):

\[ 81 \div 9 = 9 \]

So, the final answer is:

\[ 9 \]