Given the following quantities:
The total cost of the shirts is calculated as:
\(1000m + 1125n\)
The average cost per shirt is:
\(\frac{1000m + 1125n}{m + n}\)
The market price is established at 25% above the average cost. Thus, the selling price is:
\(\frac{1000m + 1125n}{m + n} \times \frac{5}{4} \times \frac{9}{10}\)
Upon simplification, the average selling price per shirt is:
\(\frac{9}{8} \times \frac{1000m + 1125n}{m + n}\)
The average profit per shirt is determined by:
\(\frac{1}{8} \times \frac{1000m + 1125n}{m + n}\)
The total profit for all shirts is:
\(\frac{1}{8} \times \frac{1000m + 1125n}{m + n} \times (m + n)\)
This simplifies to:
\(\frac{1}{8} (1000m + 1125n)\)
Given that the total profit equals 51,000:
\(\frac{1}{8} (1000m + 1125n) = 51000\)
Multiplying both sides by 8 yields:
\(1000m + 1125n = 408000\)
To maximize the total number of shirts (\( m + n \)), we must minimize \( n \), with the constraint that \( n \) cannot be zero. Consequently, \( m \) must be maximized.
The equation is rearranged to solve for \( m \):
\(m = \frac{408000 - 1125n}{1000}\)
By minimizing \( n \) and maximizing \( m \), inspection reveals the maximum value for \( m \) to be 399 and for \( n \) to be 8.
The total number of shirts is then:
\(m + n = 399 + 8 = 407\)
The maximum number of shirts achievable is \( \boxed{407} \).
The correct option is (B): 407.