Box 1: one instance
Refer to scaling condition provided in the question, August 8, 2018 is outside the schedule of the scale condition 1, and Default instance count is 1.
Box 2: two instances
The default instance count is important because autoscale scales your service to that count when metrics are not available. Therefore, select a default instance count that's safe for your workloads.
The Default instance count of scale condition 1 is 4, and the Scale in rule decreases the count with 1.
So initial instance count before scale in condition met = 4
CPU utilization was at 15% for 60 mins so after first 10 mins ( The scale out and scale in rules are configured to have a duration of 10 minutes )instance count reduces by 1 hence after first 10 mins instance count is 4-1=3 Now cool down period is 5 mins , after first 15 mins instance count is 3 .
After next 15 mins , instance count will be 3-1=2.
After next 15 mins , instance count will be =2 because minimum instance count must be 2 , it can't get reduced beyond 2.
So after 60 mins instance count will be at 2.
Reference:
https://docs.microsoft.com/en-us/azure/azure-monitor/platform/autoscale-best-practices