Step-by-step explanation:
Let's take "a" an element from A, a ⊆ A.
As A ⊆ B, a ⊆ A ⊆ B, so a ⊆ B.
Therefore, a ⊆ B ⊆ Cc, a ⊆ Cc.
Let's remember that Cc is exactly the opposite of C. That means that an element is in C or in Cc; it has to be in one of them but not in both.
As a ⊆ Cc, a ⊄ C.
As we can generalize this for every element of A, there is not element of A that is contained in C.
Therefore, the intersection (the elements that are in both A and C) is empty.
