For item a) we need to find the maxima of a function. If we take the derivative of a function, when its equal to 0, it could be a maxima or a minima
Let's take the derivative:
[tex]P(q)=-0.01q^2+3q-37[/tex]
By using the derivative rules:
[tex]\begin{gathered} P^{\prime}(q)=-0.01\cdot2\cdot q+3 \\ P^{\prime}(q)=-0.02q+3 \end{gathered}[/tex]
Now, by making the derivative equal 0, we can find the critic points:
[tex]\begin{gathered} \text{If}P^{\prime}(q)=0 \\ \text{Then:} \\ 0=-0.02q+3 \end{gathered}[/tex]
And solve for q:
[tex]\begin{gathered} \frac{-3}{-0.02}=q \\ q=150 \end{gathered}[/tex]
We can infer that the function P(q) has a critical point in q = 150. To know what is the nature of that critical point, we can take the second derivative:
[tex]P^"(q)=-0.02[/tex]
Since the second derivative is negative, the point q = 150 is a maximum.
Thus, the answer to question a is
Answer: 150 thousand pairs of sunglasses needs to be sold.
Now to part b)
Since the maximum profit will occur when q = 150, to know the maximum profit, we need to evaluate P(q) when q = 150:
[tex]P(150)=-0.01(150)^2+3\cdot150-37[/tex]
Solving:
[tex]\begin{gathered} P(150)=-225+450-37 \\ P(150)=188 \end{gathered}[/tex]
The answer to b is:
Answer: 188 thousand dollars of maximum profit can be expected