E = [4, 0, 0]
M = 1/2·([4, 0, 13] + [0, 6, 13]) = [2, 3, 13]
P = [0, 6, z]
EM = [2, 3, 13] - [4, 0, 0] = [-2, 3, 13]
MP = [0, 6, z] - [2, 3, 13] = [-2, 3, z - 13]
EM ⊥ MP --> [-2, 3, 13]·[-2, 3, z - 13] = 13·z - 156 = 0 --> z = 12
P = [0, 6, 12]
|EP| = |[0, 6, 12] - [4, 0, 0]| = |[-4, 6, 12]| = 14 LE