Show that if A ⊂ B, then C - B ⊂ C - A

Show that if A ⊂ B, then C - B ⊂ C - A.

Answer
Let x ∈ C - B
x ∈ C and x ∉ B
Given that [A ⊂ B] so that if any element doesn’t lies in set B then it cannot be in set A.
x ∈ C and x ∉ A
x ∈ C - A
Hence, C - B ⊂ C - A.