It seems like you're calculating the arithmetic mean (average) of the numbers 7, 2, 9, and 8. Here's a clearer breakdown of the calculation:

1. The sum of the numbers:
   $7 + 2 + 9 + 8 = 26$

2. The number of terms:
   There are 4 terms in total.

3. The arithmetic mean (average) is calculated by dividing the sum by the number of terms:
   $\frac{26}{4} = 6.5$

Thus, the mean $X_1$ is $6.5$.

Would you like any further details or have any questions about the steps? Here are some related questions:

1. How is the arithmetic mean useful in data analysis?
2. Can the arithmetic mean be misleading? In which cases?
3. How does the mean differ from the median?
4. What is the geometric mean, and how is it calculated?
5. How can outliers affect the arithmetic mean?

Tip: Always make sure to double-check your arithmetic when performing calculations manually to avoid small errors.