If you draw this out you will see this is a parabola lying on its side opening out to the right. The conic equation therefore is 4p(x-h) = (y-k)^2 where h and k are the coordinates of the vertex and p is the focal distance (4) which gives us (4)(4)(x)= y^2 y^2 = 16x
You will also see from inspection that as x increases so does y. You can graph this in desmos . So the widest point will be at x= 8 y^2 = 16 x 8 y^2 =128 y= 13.3137
since the parabola is symetric the total width will be twice this or 22.63 rounded to the nearest hundreth