Find VM if the dihedral angle formed by the intersection of ABCD and triangle VB

Find VM if the dihedral angle formed by the intersection of ABCD and triangle VB

Given:  Square ABCD and each side is 16

             Equilateral triangle is VBC

  M is the midpoint of AD

What is the length of VM if the dihedral angle formed by the intersection of triangle VBC and ABCD is 30 degrees?

is 90 degrees? is 0 degrees?  is n degrees?20150321_174209.jpg 20150321_173900.jpg 20150321_173825.jpg 

Ignore everything that is handwritten in the table