ABC forms a right angled triangle since ($12^{2} + 5^{2} = 13^{2}$)
Area of triangle ABC = 0.5 * 12 * 5 = 30
As given in Question (A rectangle is constructed which is equal in area to the triangle)
Let L be the length of the rectangle and width of 10 units.
Then , area of rectangle = 30 = 3 * 10 = L * 10
So L = 3 units
Perimeter of rectangle = 2(10 + 3) = 26.
Hence B is the Correct option.