Oliver works at a bookstore. He packed 20 identical paperbacks and 9 identical textbooks in a box. The total mass of the books was 44.4 pounds. After he put 1 more textbook and 5 more paperbacks in the box, the total mass of the books was 51 pounds.
Write a system of equations that can be used to determine p, the mass, in pounds, of one paperback, and t, the mass, in pounds, of one textbook.