Good morning!
Cost:
[tex]C(x)=2x+26[/tex]
Price:
[tex]p(x)=30-2x[/tex]
R(x):
[tex]R(x)=xp(x)=x(30-2x)=30x-2x^2[/tex]
Calculating the profit function:
[tex]P(x)=R(x)-C(x)=30x-2x^2-(2x+26)\\P(x)=-2x^2+28x-26[/tex]
To maximize profit:
[tex]P'(x)=0\\-4x+28=0\\x=7[/tex]
Max-Profit:
[tex]P(7)=-2(7)^2+28(7)-26=-2(49)+196-26=72[/tex]
I hope I have helped!