Read the passage below and choose one correct answer for each question.

Books which give instructions on how to do things are very popular in the United States today. Thousands of these How-to books are useful: in fact, there are about four thousand books with titles that begin with the words 'How-to". One book may tell you how to earn more money, another may tell you how to save or spend it and another may explain how to give your money away. Many How-to books give advice on careers. They tell you how to choose a career and how to succeed in it. If you fail, however, you can buy the book “How to Turn Failure into Success”. If you would like to become very rich, you can buy the book “How to Make a Millionaire”. If you never make any money at all. you may need abook called “How to Live on Nothing”. One of the most popular types of books is one that helps you with personal problems. If you want to have a better love of life, you can read “How to Succeed in Love Every Minute of Your Life”. If you are tired of books on happiness,  you may prefer books which give step-by-step instructions on how to redecorate or enlarge a house. Why have How-to books become so popular? Probably because life has become so complex. Today people have far more time to use, more choices to make, and more problems to solve. How-to books help people deal with modern life.

The passage tells us that How-to books sell well on how________.