Answer
vertex: $( -9,-388)$
Work Step by Step
Consider the equation: $y=x^2+18x-307$ ...(1)
The standard equation of the parabola is: $y=a(x-h)^2+k$ with vertex$(h,k)$
Consider right side $x^2+18x=307$
To complete the square add $(\frac{b}{2})^2=(\frac{18}{2})^2=81$.
$x^2+18x+81=307+81$
$(x+9)^2=388$
Thus, equation becomes:
$y=(x+9)^2-388$
Compare it with the standard form of the parabola, we get
vertex: $( -9,-388)$
