To order 2 books: $21.91 [$18.00 + $3.91 shipping]
To order 3 books: $30.91 [$27.00 + $3.91 shipping]
To order 4 books: $40.32 [$36.00 + $4.32 shipping]
To order 5 books: $49.32 [$45.00 + $4.32 shipping]
To order 6 books: $58.73 [$54.00 + $4.73 shipping]
To order 7 books: $68.14 [$63.00 + $5.14 shipping]