A book costs $4 more than a CD. The CD is 30% cheaper than a $20 album. How much does the book cost? Let's be accurate as possible.
The CD is 30 / 100 * 20 = $6 cheaper than the album. So the cost of the CD is 20 - 6 = $14. The book is $4 more expensive than the CD, which means it cost 14 + 4 = $18.
The answer: 18.