Let's consider the equation of parabola, y = a·(x - α)·(x - β)
where α, β are the x-intercepts.
From the given graph, the y-intercept is (0, -3).
From the given graph, the x-intercept are (-1, 0) and (3, 0) i.e. α = -1, β = 3.
So the equation of parabola would be now, y = a·(x + 1)·(x - 3)
We can plug the y-intercept (0, -3) in the equation to find value of 'a'.
-3 = a·(0+1)·(0-3)
-3 = -3a
a = 1
So the equation of parabola would be now, y = (x + 1)·(x - 3) = x² - 2x - 3
Comparing it with y = ax² + bx + c
The x-coordinate of vertex would be, 
the y-coordinate of vertex would be, y = (1)² - 2(1) - 3 = -4.
Hence, vertex would be (1, -4).
