Explanation:
the vertex form of a quadratic function is
y = (x - h)² + k
with (h, k) being the vertex.
luckily for us the function is already defined in that form.
so, when we compare
y = (x + 4)² - 9
with the general form about (h, k) above we see
h = -4
k = -9
so, the vertex is (-4, -9).