Question 1103716
I assume you mean -x^2(?).
Convert to vertex form to find the maximum.
{{{P(x)=-x^2+80x+63}}}
{{{P(x)=-(x^2-80x+40^2)+63+40^2}}}
{{{P(x)=-(x-40)^2+1663}}}
The maximum occurs at the vertex (40,1663).