Answered by Gary Ward, Quora, MaEd Education & Mathematics, Austin Peay State University (1997)
Label the vertices A (2,4), B (2,0), C (0,-4) and D (4,-4).
Since only two dimensions are given for a 3D figure, this is a degenerate tetrahedron with four faces ACD and ADB, DCB and CAB going clockwise.
Due to its unique geometry, the area of ACD = ADB + DCB + CAB, so the total area equals 2 · Area_ACD.
A = 2(½ · b · h) = 2(½ · 4 · 8) = 32 units²
Explanation of degenerate tetrahedron: Since a tetrahedron is a three-dimensional figure, count the area of all four faces, even though the volume is zero. If the question had just asked for the area of the figure meaning two-dimensional, it would be 16 units².
The total area of the degenerate tetrahedron is 32 square units.