There are two triangular faces and three rectangular faces.
The triangular faces are congruent, so they have the same area. We calculate one and we'll know both.
The three rectangles are different.
Triangular face (each)
Although you can hardly see in the colored figure, there is a small symbol on the right side showing that the 4 km side and the 3 km side of the triangles are perpendicular. That means those sides are the base and the height.
A = (1/2)bh = (1/2)(3 km)(4 km) = 6 km^2
Rectangular faces:
A = LW = 7 km * 3 km = 21 km^2
A = LW = 7 km * 5 km = 35 km^2
A = LW = 7 km * 4 km = 28 km^2
total surface area = 2 * 6 km^2 + 21 km^2 + 35 km^2 + 28 km^2
total surface area = 96 km^2
