Answer:
6,840 casts
Step-by-step explanation:
Assuming that every actor can play each of the 4 roles and that each role is different, the number of possible casts including at least one of sir Ian and Patrick is given by the total number of possible casts (permutation of 4 out of 12 actors), minus the number of casts without sir Ian and Patrick (permutation of 4 out of 10 actors):
There are 6,840 possible casts.