Answer: Option 'c' is correct.
Step-by-step explanation:
Since we have given that
[tex]P(x)=-0.004x^2+2.8x-350[/tex]
So, we will first derivative it w.r.t to x, we get that
[tex]P'(x)=-0.008x+2.8[/tex]
For critical points, we get that
[tex]P'(x)=0\\\\-0.008x+2.8=0\\\\-0.008x=-2.8\\\\x=\dfrac{2.8}{0.008}\\\\x=350[/tex]
Now, we will check for maximum profit.
So, we will find Second derivation and then put the value of x = 350 in it.
[tex]p''(x)=-0.008<0[/tex]
So, it will give maximum profit.
Hence, At 350 pretzels, there must be maximum profit.
Therefore, Option 'c' is correct.