For x values 1 unit either side of the vertex, the value of y is 2 more than it is at the vertex.
a = 2
_____
More formally, The graph appears to go through the point (4, 1). Substituting these values for (x, y) in the equation, we get
1 = a(4-3)² -1 . . . . substitute for x and y
2 = a . . . . . . . . . . add 1 and simplify