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The question is not clear.

I assume that we are talking about the square faces on the surface of cube.

There are six square surfaces: On each surface there are two diagonals intersecting and they divide the square in to 4 equal triangles. 

We can combine two adjacent triangles and we get 4 more triangles.

Each cube has  (4+4) * 6 = 48 triangles.

Totally there are  48 * 4000 = 1,92,000 triangles.

I assume we are not to worry about the diagonals inside the cube - that can be  between diametrically opposite corners on different surfaces. actually 4 diagonals can be drawn inside the cube meeting at the center of the cube. they also form 8 *2 =16 triangles (bigger than on the surfaces). If this number is included then we get 64,000 more triangles.