Hi @Akhil raja rao K,
You can do this using labels, a Statistics Collector, and a Calculated Table. Let me explain each in some detail, then if you have questions, you can ask for more specifics.
LABELS:
The person flow items in your model need labels assigned when they arrive at and leave each area. This is done with OnEntry and OnExit triggers on the waiting lines. The A1Entry and A1Exit labels for the area 1 waiting line are assigned in the OnEntry and OnExit triggers, respectively. The labels are a time value. Also included on the OnExit trigger is a calculation of the total time spent at the waiting line, which is just the difference between the two labels.

STATISTICS COLLECTOR:
The Statistics Collector listens to the person flow items being destroyed (or you could listen elsewhere, but the sink was easier) at the "Remove Person" activity in Process Flow. Every time a token passes through this activity, the Statistics Collector takes the person's calculated labels of time spent in each area and stores them in a table. The data shape looks like the image below.

CALCULATED TABLE:
The Calculated Table runs a simple query that sums each of the columns: A1Time, A2Time, and A3Time. This makes it possible to read the data in a pie chart. The query setup is shown in the next image. The pie chart setup should be fairly straightforward.

Here's the updated model: pie-charts-for-areas.fsm Note that your model is throwing lots of errors on the animations... might be worth looking into that as well.
Hope this helps!