If the origin is

Since, centroid of a triangle is found by

The points are A(a,1,3) and B(-2, b, -5), and its centroid is (0, 0, 0) and its third vertex C(4,7,c).

Using the formula, we get

Equating it with the coordinates of centroid, we get

a = -2

b = -8

and,

c = 2

therefore, a= -2, b= -8, c=2.