Translate each of the following statements into an equation:

A. The perimeter (p) of an equilateral triangle is three times of its side(a).

B. The diameter (d) of a circle is twice its radius (r).

C. The selling price (s) of an item is equal to the sum of the cost price (c) of an item and the profit (p) earned.

D. Amount (a) is equal to the sum of principal (p) and interest (i).