If you want to find the area of the front surface of a box, you're trying to calculate the area of one side. I don't understand the steps you used in your explanation. The area of one side is the multiplication of the length times the width. The product is the area of the surface in square units.

I don't think you have given enough data. For calculating the area of the front surface of the box you need to know its length and breadth. You have talked about the length and the height. You don't require the height but breadth to calculate the surface area. So none of the option is correct .

HOWEVER, IF THE BOX IS A CUBE IN SHAPE THEN ALL OF ITS DIMENSIONS (LENGTH,BREADTH & HEIGHT) WILL BE SAME. IN THAT CASE SQUARING ONE SIDE OF THE BOX WILL GIVE THE SURFACE AREA.

HOWEVER, IF THE BOX IS A CUBE IN SHAPE THEN ALL OF ITS DIMENSIONS (LENGTH,BREADTH & HEIGHT) WILL BE SAME. IN THAT CASE SQUARING ONE SIDE OF THE BOX WILL GIVE THE SURFACE AREA.