Note that Profit = Revenue - Cost
From the problem, we have :
Revenue = d(14.5 - 0.00003d)
and
Cost = 10,500 + 3.9d
The profit function will be :
[tex]\begin{gathered} \text{Profit}=\text{Revenue}-\text{Cost} \\ \text{Profit}=d(14.5-0.00003d)-(10500+3.9d) \\ \text{Profit}=14.5d-0.00003d^2-10500-3.9d \\ \text{Profit}=-10500+10.6d-0.00003d^2 \end{gathered}[/tex]
Substitute d = 30,000
[tex]\begin{gathered} \text{Profit}=-10500+10.6d-0.00003d^2 \\ \Rightarrow-10500+10.6(30000)-0.00003(30000)^2 \\ \Rightarrow280500 \end{gathered}[/tex]
Answer :
C. $280,500