P(A∪B) = , P = → (Given)

Now,

P = P(A∩B) → (1)

P(A∩B) = 1 - P(A∩B)

→ From (Given) & (1)

Also,

P = 1 – P(A) → (2)

P = 1 – P(B) → (3)

Now, according to the addition theorem of probability:

P(A⋃B) = P(A) + P(B) – P(A⋂B)

→ From (2) & (3)