Acertain bookstore chain has two stores, one in san francisco and one in los angeles. it stocks three kinds of books: hardcover, softcover, and plastic (for infants). at the beginning of january, the central computer showed the following books in stock. hard soft plastic san francisco 1,000 3,000 6,000 los angeles 1,000 6,000 3,000 its sales in january were as follows: 600 hardcover books, 1,300 softcover books, and 2,000 plastic books sold in san francisco, and 400 hardcover, 300 softcover, and 500 plastic books sold in los angeles. the bookstore chain actually maintained the same sales figures for the first 6 months of the year. each month, the chain restocked the stores from its warehouse by shipping 500 hardcover, 1,500 softcover, and 1,500 plastic books to san francisco and 600 hardcover, 600 softcover, and 600 plastic books to los angeles. (a) use matrix operations to determine the total sales over the 6 months, broken down by store and type of book.