To find the mean (average) of a set of numbers, you follow these steps:

1. Add all the numbers together.
2. Divide the sum by the total number of values in the set.

Given the numbers:
7, 7, 17, 18, 13, 33, 6, 12, 11, 6, 3, 11, 15, 26, 12

Step 1: Add all the numbers together.

$7 + 7 + 17 + 18 + 13 + 33 + 6 + 12 + 11 + 6 + 3 + 11 + 15 + 26 + 12 = 197$

Step 2: Divide the sum by the total number of values (there are 15 numbers).

$\frac{197}{15} = 13.13\ (rounded\ to\ two\ decimal\ places)$

So, the mean is 13.13.

Would you like more details or have any questions?

Here are 5 related questions:

1. What is the median of this dataset?
2. How would you find the mode of these numbers?
3. How does the mean change if you add another number to this list?
4. What is the difference between the mean and the median?
5. Can outliers affect the mean significantly?

Tip: The mean is sensitive to extreme values (outliers), while the median is more robust in such cases.