The profit is computed as follows:
Profit = price - cost
Substituting with:
[tex]\begin{gathered} \text{price}=p(x)=1115-0.09x^2 \\ \text{ cost =c}(x)=840+385x \end{gathered}[/tex]we get:
[tex]\begin{gathered} P(x)=p(x)-c(x) \\ P(x)=1115-0.09x^2-(840+385x) \\ \text{Combining similar terms:} \\ P(x)=1115-0.09x^2-840-385x \\ P(x)=-0.09x^2-385x+1115-840 \\ P(x)=-0.09x^2-385x+275 \end{gathered}[/tex]