If you are looking for x then it is X = 18
Answer: -216
Step-by-step explanation:
To solve the exercise you must use the formula shown below:

Where:

You should find 
The formula to find it is:

Where d is the difference between two consecutive terms.

Then:

Substitute it into the first formula. Therefore, you obtain:

The age of the students is about 0.67 years away from the 13.3 years.
The Mean Absolute Deviation is the average distance away from the mean. For the last choice, you should select more variable. Since the average is higher, there is a greater distance between the points and the mean.