Final answer:
The value for week 3 in the given time series data is 16.
Step-by-step explanation:
The value for week 3 in the given time series data is 16. When working with time series data, each value corresponds to a specific time period—in this case, weekly data. Therefore, for week 1 the value is 18, week 2 is 13, and consequently, for week 3, the correct value is 16.