Answer :
[tex]\begin{gathered} \text{The quadratic equation is,} \\ y=-35x^2+1458x-8400 \\ \text{for maxi}mum\text{ amount,} \\ \frac{dy}{dx}=0 \\ \frac{d(-35x^2+1458x-8400)}{dx}=0 \\ -70x+1458=0 \\ x=\frac{1458}{70} \\ x=20.82 \\ So,\text{ the maxi}mum\text{ profit,} \\ y=-35(20.82)^2+1458(20.82)-8400 \\ y=\text{ \$6772 (Profit)} \end{gathered}[/tex]