Regular pentagon means the shape with 5 sides which their lengths are equal to each other.
so, if the total perimeter of the pentagon is 10s - 20,
we can find the length of each side by dividing it by 5.
(10s - 20) / 5
we can expand this equation by dividing each number in the bracket by 5
= 2s - 4
Therefore, the answer should be D.
