Question 327106
If I understood your question correctly as typed, the vertex should be at the origin or at the point (0,0).  This parabola opens upward and so it has the form
x^2 = 4Py.

Let P = distance of vertex from focus

The parabola is 8 feet wide and 3.5 feet.

This means that the end points are (-4,3.5) and (4,3.5).

We use the point (4,3.5) which has a positive x-coordinate since we are dealing with distance and distance is a positive measure.

x^2 = 4Py

(4)^2 = 4P(3.5)

16 = 14P

16/14 = P

The focus is at the point (0,P), which is P units from the vertex's origin location (0,0).

The focus should be 16/14 feet or about 1.14 feet from the vertex.