we are told that the revenue is
this is a quadratic function, so to maximize it we should find the x-value of its vertex. recall that the x-value of the vertex of the parabola ax^2+bx+c is given by the formula −b/2a.
so in this case, we have a=−10 and b=4080, so the x-value of the vertex is
thats not a system of equations, that is a solution