Final answer:
Option b, which suggests calling the taxpayer for clarification, is the most responsible decision to ensure accuracy while addressing the taxpayer's unclear request.
Step-by-step explanation:
When handling a taxpayer's written request that is unclear and lacks necessary information, the professional and responsible decision would be option b: Call the taxpayer for clarification. While pressure to increase case resolution numbers is high, it's important to balance efficiency with accuracy and customer service.
A phone call provides direct communication, ensuring that accurate information is gathered and can potentially resolve the issue in one interaction, rather than risking an incorrect assumption which could lead to additional interest being assessed on the account.
If making a call is too time-consuming, sending a letter to the taxpayer (option a) requesting additional information would be the next best step, encouraging accuracy and a clear paper trail. Making assumptions (option c) is risky and could exacerbate issues, and escalating to a supervisor (option d) may be unnecessary at this initial stage of information gathering.