Answer:
the equation of the axis of symmetry is 
Step-by-step explanation:
Recall that the equation of the axis of symmetry for a parabola with vertical branches like this one, is an equation of a vertical line that passes through the very vertex of the parabola and divides it into its two symmetric branches. Such vertical line would have therefore an expression of the form:
, being that constant the very x-coordinate of the vertex.
So we use for that the fact that the x position of the vertex of a parabola of the general form:
, is given by:

which in our case becomes:

Then, the equation of the axis of symmetry for this parabola is:

The answer would be three. The reasons are clear. You can't form a closed figure when you just have two sides. All they would do is just intersect each other. Also, one side must intersect with two other noncollinear sides. This means that a polygon has to have at least three sides.
16/5 is roughly equal to 3.2. Is that what your are asking?
B.) a=-5.7
1.6(a)=-9.12
(a)=(-9.12)/(1.6)
a=-5.7