- Given that the 11 natural numbers are \( x_1, x_2, ..., x_{11} \) arranged in ascending order.
- The average of the first six numbers is 18, so their sum is:
\[ \text{Sum of first 6 numbers} = 6 \times 18 = 108 \]
- The average of the last six numbers is 28, so their sum is:
\[ \text{Sum of last 6 numbers} = 6 \times 28 = 168 \]
- The 7th number \(x_7\) is the smallest prime number greater than 20, which is 23. Hence,
\[ x_7 = 23 \]
- Now, the sum of all the numbers is:
\[ \text{Sum of all 11 numbers} = 108 + 168 + 23 = 299 \]
Conclusion: The sum of all these numbers is 299.