## Algebra 2 (1st Edition)

The number of boxes of books is $8$ and the number of boxes of clothes is $12$.
Let $x$ be the number of boxes of books. Then the number of boxes of clothes is $20-x$. Then our equation is: $40x+(20-x)7=404\\40x+140-7x=404\\33x=264\\x=8$. Thus the number of boxes of books is $8$ and the number of boxes of clothes is $12$.