A median of a tetrahedron is a segment joining a vertex to the centroid of the opposite

Question:

A median of a tetrahedron is a segment joining a vertex to the centroid of the opposite face. The tetrahedron in Figure 22(B) has vertices at the origin and at the terminal points of vectors u, v, and w. Show that the medians intersect at the terminal point of 1/4 (u + v + w).

u W (B)