Given data P(A) = 0.25 , P(B) = 0.45  and  P( A∩B ) = 0.15

Apply formula: P( AUB ) = P(A) + P(B) − P( A∩B )

Substitute : P(A) = 0.25 , P(B) = 0.45 and P( A∩B ) = 0.15

P( AUB ) = 0.25 + 0.45 - 0.15

P( AUB ) = 0.55

P( AUB ) = 0.55.