Final answer:
The correct Standard Subject Identification Code (SSIC) number to use when preparing a Letter-Type Directive is SSIC 5215, which helps organize official communications in the U.S. Navy.
Step-by-step explanation:
When preparing a Letter-Type Directive, each instruction and notice issued shall be assigned a Standard Subject Identification Code (SSIC) number. The correct SSIC to use in this scenario is from SSIC 5215. The SSIC is used across the U.S. Navy's filing system to categorize and organize official communications and directives. Therefore, the answer to your question is b) SSIC 5215.