Write the following using numbers, literals and signs of basic operations State what each letter represents: The diameter of a circle is twice its radius. The area of a rectangle is the product of its length and breadth. The selling price equals the sum of the cost price and the profit. The total amount equals the sum of the principal and the interest. The perimeter of a rectangle is two times the sum of its length and breadth. The perimeter of a square is four times its side.