Answer:
The difference between the total and lateral surface areas of the room is 42 square yards.
Explanation:
The lateral surface area of an object is the surface area of everything EXCEPT for the top and bottom of the object.
2(6*4.2) + 2(4.2*3.5) = 79.8 square yards
The total surface area of an object is everything INCLUDING the top and bottom of the object.
79.8 + 2(6*3.5) = 121.8 square yards
121.8 - 79.8 = 42 square yards