A university has two departments, Department A and Department B. Department A has 4 sections, with 20 students in each section. 40% of the students in Department A are seniors. Department B has 6 sections, with 15 students in each section. 60% of the students in Department B are seniors. If a student is chosen at random from these departments and is found to be a senior, what is the probability that the student is from Department B?