The total area of a box is the sum of all the area of the faces it has. It is also called the surface area. The area of one face of a rectangular box is equal to the product of its length and width. So, the total area would be:
SA = 2lw + 2wh + 2lh
SA = 2(4)(3) + 2(3)(6) + 2(4)(6)
SA = 108 ft^2