Focal distance of an ellipse is given by the formula
[tex]f = ae[/tex]
here a = length of semi major axis
e = eccentricity of the path
now here we know that
length of major axis for the path of planet is given as 32 units
so here we can say
[tex]2a = 32 units[/tex]
[tex]a = 16 units[/tex]
so length of semi major axis is 16 units
focal distance for the planet path is given as 8 units
now from the above formula we can write
[tex]f = a*e[/tex]
[tex]8 = 16*e[/tex]
[tex]e = \frac{8}{16}[/tex]
[tex]e = \frac{1}{2} = 0.5[/tex]
so eccentricity for the path of planet will be 0.5
