unable to understand data fetch dates span

Can someone help me understand what dates the below query is expected to fetch data for, and why ?

##azure cost management api 

let
billingProfileId = "<<Billing Profile Id>>",
optionalParameters1 = [startBillingDataWindow = "-9", endBillingDataWindow = "-6"],
source1 = AzureCostManagement.Tables("Billing Profile Id", billingProfileId, 5, optionalParameters1),
riusagedetails1 = source1{[Key="riusagedetails"]}[Data],
optionalParameters2 = [startBillingDataWindow = "-6", endBillingDataWindow = "-3"],
source2 = AzureCostManagement.Tables("Billing Profile Id", billingProfileId, 5, optionalParameters2),
riusagedetails2 = source2{[Key="riusagedetails"]}[Data],
riusagedetails = Table.Combine({riusagedetails1, riusagedetails2})
in
riusagedetails