The way I picture this thing, it's made of three rectangles
that are joined together.
-- One rectangle is 3 x 6 meters.
-- One rectangle is 3 x 8 meters.
-- One rectangle is 3 x 10 meters.
-- Their 3-meter edges are all taped together to make a 'tube'.
-- It's 3 meters long, and it has 3 sides.
-- When you look at the ends of the tube, they're both
right triangles with sides of 6, 8, and 10 meters.
-- The area of each side = 1/2 (base x height)
= 1/2(6m x 8m) = 24 square meters.
2 ends = 48 square meters.
-- The lateral surface area is the area of the three rectangles
that make the 'tube'.
-- Area of the 6 x 3 rectangle = 18 square meters
-- Area of the 8 x 3 rectangle = 24 square meters
-- Area of the 10 x 3 rectangle = 30 square meters
-- Total lateral area = (18 + 24 + 30) = 72 square meters.
-- When you add the ends to it, you get
(72 + 48) = 120 square meters
for the total area.