Seven boxes, D, E, F, U, V, W and X, are kept one over the other

Seven boxes, D, E, F, U, V, W and X, are kept one over the other but not necessarily in the same order. Only U is kept above D. Only V is kept between D and F. No box is kept below E. Only three boxes are kept between D and W. How many boxes are kept between X and E?

Only U is kept above D. : D, U
Only V is kept between D and F. : F, V, D, U
No box is kept below E. : E, _, _, F, V, D, U
Only three boxes are kept between D and W. : E, W, _, F, V, D, U

X will occupy vacant position :  E, W, X, F, V, D, U

Boxes are kept between X and E is One (W).