Question

The position vectors of three consecutive vertices of a parallelogram ABCD are A(4î + 2ĵ − 6k̂), B(5î − 3ĵ + k̂) and C(12î + 4ĵ + 5k̂). The position vector of D is given by

If ABCD is a parallelogram and AC and BD are its diagonals, then AC + BD is :