Yellowstone National Park is a popular field trip destination. This year the senior class at High School A and the senior class at High School B both planned trips there. The senior class at High School A rented and filled 12 vans and 6 buses with 306 students. High School B rented and filled 12 vans and 9 buses with 369 students. Each van and each bus carried the same number of students. How many students can a van carry? How many students can a bus carry?