To calculate the firm's book value per share, we can use the following formula:

$\text{Book Value per Share} = \frac{\text{Stockholders' Equity}}{\text{Number of Common Shares Outstanding}}$

From the information provided:

• Stockholders' equity = $500,400
• Number of common shares outstanding = 120,000

Now let's calculate the book value per share:

$\text{Book Value per Share} = \frac{500,400}{120,000} = 4.17$

Thus, the firm's book value per share is $4.17.

Let me know if you need further details or explanations!

Here are 5 related questions to consider:

1. How does book value per share differ from market value per share?
2. What factors can cause stockholders' equity to change?
3. How is book value per share used by investors to assess a company's worth?
4. What role does net income play in influencing a company's equity?
5. How does the price-to-book ratio affect stock valuation?

Tip: Understanding the difference between book value and market value can give deeper insights into a company’s financial health.