To calculate the mean (average), we sum all the numbers and then divide by the total count of numbers.

Given the numbers:
5, 8, 9, 6, 5, 4, 5, 6

Step 1: Add all the numbers together: $5 + 8 + 9 + 6 + 5 + 4 + 5 + 6 = 48$

Step 2: Count how many numbers there are. There are 8 numbers in total.

Step 3: Divide the sum by the count of numbers: $\frac{48}{8} = 6$

So, the mean is 6.

The correct answer is c. 6.

Would you like further clarification or more examples on how to calculate the mean? Here are some related questions:

1. What is the median of this set of numbers?
2. How do you calculate the mode of a data set?
3. Can you find the range of the numbers provided?
4. How would you calculate the variance and standard deviation of this set?
5. What is the difference between the mean and the weighted mean?

Tip: To calculate the mean, always ensure you sum the values correctly and divide by the exact number of values in the set.