What is the eccentricity of a planet's orbit if the focal distance is 8 and the major axis is 32?

Focal distance of an ellipse is given by the formula

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

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

so eccentricity for the path of planet will be 0.5