Given:
There are given that the probability of A and probability of B.

Step-by-step explanation:
To find the value, we need to use the formula of the probability of A union probability B.
So,
From the formula:

Where,

Now,
Put all the values into the above formula:
So,
![\begin{gathered} P(AUB)=P(A)+P(B)-P(A\operatorname{\cap}B) \\ P(AUB)=0.4+0.45-0.10 \\ P(AUB)=0.75 \end{gathered}]()
Final answer:
Hence, the correct option is B.