With any fraction, no matter what its denominator (bottom part), you multiply the numerators (tops) by each other and the denominators (bottoms) by each other.
For example,
C = pi * d
a = pi * (d/2)^2
In order to know what the polygon is, you have to plot the coordinates. After plotting, it is obviously shown a form of a rectangle. After connecting the midpoints of the sides, it formed a (D) rhombus, not a kite.