Answer:
A ⊂ B ⇒ A ∩ B = A
Consider,
p ∈ A ⊂ B
x ∈ B
Let,
p ∈ A ∩ B
x ∈ A and x ∈ B
x ∈ A and x ∈ A
∴ (A ∩ B) = A