For each of the following specific audit procedures, indicate the type of audit procedure it represents: $(1)$ inspection of records or documents, $(2)$ inspection of tangible assets, $(3)$ observation, $(4)$ inquiry, $(5)$ confirmation, $(6)$ recalculation, $(7)$ reperformance, $(8)$ analytical procedures, and $(9)$ scanning.

a$.$ Sending a written request to the entity's customers requesting that they report the amount owed to the entity

b$.$ Examining large sales invoices for a period of two days before and after year$-$end to determine if sales are