Matrix Help!?!?

A cookie company makes three kinds of cookies, oatmeal raisin, chocolate chip, and shortbread packaged in small medium and large boxes. The small box contains one dozen oatmeal raisin and one dozen chocolate chip. The medium box contains two dozen oatmeal raisin, one dozen chocolate chip, and one dozen shortbread. The large box contains two dozen oatmeal raisin, two dozen chocolate chip and three dozen shortbread. If you require exactly 15 dozen oatmeal raisin, 10 dozen chocolate chip and 11 dozen shortbread, how many of each box should you buy?

solve using the matrix method. (row reduction?)