You cannot divide a vector by a vector:

Plane.Position = PlaneA.Position / PlaneB.Position;

However, you can multiply and divide a vector with a scaler ( = number ). This is done for every component:

// every component of Plane.Position will be twice as large:

Plane.Position = PlaneA.Position * 2;

// every component of PlaneB.Position will be half as large:

PlaneB.Position = PlaneA.Position / 2;