A course has two teaching assistants. If a student's assignment goes to Adam, then there is 60% chance that they get a grade higher than a B+, and if the assignment goes to Barbie then there is a 50% chance that the grade will be higher than a B+. Suppose that Barbie grades 75% of all the assignments.
What is the probability that a student will have a grade higher than a B+ and it was marked by Barbie?