I found my coworker’s W-2 in a book — she makes $15,000 more than me for the same job. What should I do?

A worker discovered a coworker's W-2 form in a book, revealing a $15,000 salary difference for the same job, prompting questions about self-advocacy. The worker is unsure how to approach the situation without appearing whiny. The discovery has led to concerns about fair compensation.