Answer:
It looks like (x - 5)^2 - 7 is correct.
Explanation:
The vertex form of this type of function is
a(x - b)^2 + c where a is some constant and (b, c) is the vertex.
In this case the vertex is at (5, -7) so we can write f as:
a(x - 5)^2 - 7.
From the diagram it looks like when x = 0 f lies between 16 and 20 so that makes a = 1