Answer:
(
a
−
1
+
b
)(
a
−
1
−
b
)
.
Divide the limit by the weight of one book to find the number of books allowed.
70/12 = 5.833 books
You cannot send a part of a book, so round down. The answer is 5 books.
55,000÷0.04
=1,375,000
55,000÷0.02
=2,750,000
2,750,000−1,375,000
=1,375,000 increase