Mean-Deviation:
Mean deviation, also known as the mean absolute deviation (MAD), is a measure of the spread or dispersion of a set of data points. It is calculated by finding the average of the absolute differences between each data point and the mean of the data set.

Calculating the Mean:
To calculate the mean of a set of data, add up all the values and divide by the total number of values.

In this case, we have the following data: 3, 5, 6, 7, 8, 10, 11, 14

To find the mean, we add up all the values:
3 + 5 + 6 + 7 + 8 + 10 + 11 + 14 = 64

Then, we divide by the total number of values, which is 8:
64 / 8 = 8

So, the mean of the given data is 8.

Calculating the Mean-Deviation:
To calculate the mean-deviation, we need to find the absolute difference between each data point and the mean, and then find the average of these absolute differences.

The absolute difference between each data point and the mean is calculated by subtracting the mean from each data point and taking the absolute value of the result.

For example, for the first data point 3:
|3 - 8| = 5

Similarly, we calculate the absolute differences for all the data points and find their average.

|3 - 8| = 5
|5 - 8| = 3
|6 - 8| = 2
|7 - 8| = 1
|8 - 8| = 0
|10 - 8| = 2
|11 - 8| = 3
|14 - 8| = 6

Now, we find the average of these absolute differences:
(5 + 3 + 2 + 1 + 0 + 2 + 3 + 6) / 8 = 22 / 8 = 2.75

Therefore, the mean-deviation of the given data is 2.75.

Conclusion:
The correct answer is option 'C' (2.75) as the mean-deviation of the data 3, 5, 6, 7, 8, 10, 11, 14 is 2.75.