Silent Letters Have No Figure Value
In addition to a, e, i, o, u, and w, h, and y, which have no figure value, all silent letters have none, because they are not SOUNDED. SOUND is the one and only indicator of digit value.
NIGHT is 21 for the GH is silent.
KNIFE is 28 for the K is silent.
MADGE is 36 for the D is silent.