We have been given that the profit that the vendor makes per day by selling x pretzels is given by the function
. We are asked to find the number of pretzels that must be sold to maximize profit.
First of all, we will find the derivative of our given function.
![P'(x)=-4\cdot 2x^(2-1)+2400](https://img.qammunity.org/2021/formulas/mathematics/college/77r90dybeut486w4qzytnskbrqtvm13m98.png)
![P'(x)=-8x+2400](https://img.qammunity.org/2021/formulas/mathematics/college/5oihfron7cyfyq89c91qae9q3i14s3dwj8.png)
Now, we will find the critical point by equating derivative with 0 as:
![-8x+2400=0](https://img.qammunity.org/2021/formulas/mathematics/college/ttqxbvhcyku8r50rvok8ifls8tt3ilxqbl.png)
![-8x+2400-2400=0-2400](https://img.qammunity.org/2021/formulas/mathematics/college/9f2w84i1awvhdsmtdamk0xn07n378nbb17.png)
![-8x=-2400](https://img.qammunity.org/2021/formulas/mathematics/college/j96lo45xdta91j0chwb5kf1hx67tevm8kf.png)
![(-8x)/(-8)=(-2400)/(-8)](https://img.qammunity.org/2021/formulas/mathematics/college/incyc5r5jd2lgb60fhx3o1kljjfedtv5x8.png)
![x=300](https://img.qammunity.org/2021/formulas/mathematics/middle-school/bxsgh4zz9v1j3xei34oql70gicdjqkihhk.png)
Therefore, the company must sell 300 pretzels to maximize profit and option B is the correct choice.