Answer :

Let's simplify the expression \(\left(\frac{3}{x}\right)^4\) step by step.

1. Initial Expression:
[tex]\[ \left(\frac{3}{x}\right)^4 \][/tex]

2. Applying the Exponent:
When you raise a fraction to a power, you apply the exponent to both the numerator and the denominator. So,
[tex]\[ \left(\frac{3}{x}\right)^4 = \frac{3^4}{x^4} \][/tex]

3. Calculating the Exponents:
Calculate \(3^4\):
[tex]\[ 3^4 = 3 \times 3 \times 3 \times 3 = 81 \][/tex]
The \(x^4\) term remains as it is:
[tex]\[ x^4 \][/tex]

4. Final Simplified Expression:
Combine the results from the numerator and the denominator:
[tex]\[ \frac{3^4}{x^4} = \frac{81}{x^4} \][/tex]

So, the simplified expression is:
[tex]\[ \frac{81}{x^4} \][/tex]

We can write it as \(\frac{81}{x}\). Therefore, the answer to what should be written in the numerator is 81.

[tex]\[ \frac{81}{x^4} \][/tex]