Answer:
P(B)= 0.305
Step-by-step explanation:
Hello!
This exercise is an application of conditional probabilities.
You know that the definition of a conditional probability is:

And
The probability of A occuring, given that B has already ocurred is P(A/B)= 0.61
The probability of A and B ocurring at the same time is P(A∩B)= 0.5
You can clear the probability of B from the equation:
P(B)= P(A/B)*P(A∩B)= 0.61*0.5= 0.305
I hope you have a SUPER day!