Since the cost function is
[tex]C(x)=-19x^2+61000x+18324[/tex]Since the revenue function is
[tex]R(x)=-23x^2+149000x[/tex]Since the profit function is
[tex]P(x)=R(x)-C(x)[/tex]Then we will subtract C from R
[tex]\begin{gathered} P(x)=-23x^2+149000x-(-19x^2+61000x+18324) \\ P(x)=-23x^2+149000x+19x^2-61000x-18324 \end{gathered}[/tex]Add the like terms
[tex]\begin{gathered} P(x)=(-23x^2+19x^2)+(149000x-61000x)-18324 \\ P(X)=-4x^2+88000x-18324 \end{gathered}[/tex]Now, we will differentiate P(x) and equate the answer by 0 to find x maximum
[tex]\begin{gathered} P^{\prime}(x)=-4(2)x^{2-1}+88000(1)x^{1-1} \\ P^{\prime}(x)=-8x+88000 \end{gathered}[/tex]Equate P' by 0 to find x
[tex]\begin{gathered} P^{\prime}(x)=0 \\ -8x+88000=0 \end{gathered}[/tex]Subtract 88000 to both sides
[tex]\begin{gathered} -8x+88000-8000=0-88000 \\ -8x=-88000 \end{gathered}[/tex]Divide both sides by -8
[tex]\begin{gathered} \frac{-8x}{-8}=\frac{-88000}{-8} \\ x=11000 \end{gathered}[/tex]The company should produce 11000 Phones to maximize the profit