Answer:
42 yd²
Explanation:
Area of a rectangle = width x length
lateral surface area is the area of the sides only
So the difference between the total surface area and the lateral surface area would be the surface area of the ceiling and floor (top and bottom).
area of floor and ceiling = 2(3.5 x 6) = 42 yd²
Or, we can calculate the total surface area and lateral surface area, then find the difference:
total surface area = 2(3.5 x 4.2) + 2(4.2 x 6) + 2(3.5 x 6) = 121.8 yd²
lateral surface area = 2(3.5 x 4.2) + 2(4.2 x 6) = 79.8 yd²
difference = 121.8 - 79.8 = 42 yd²