A shelf support 3 3/4. If a book weighs 3/8 of a pound, how many books can I think hold? If can add more support so the shelf hold 5 1/4 pounds, how many books can the shelf hold now?

So, you want to get the mixed number, 3 3/4, as a fraction. Multiply 3 by 4 and add it to the top of the fraction, getting you the fraction 15/4. Multiply the top and bottom by 2, getting the denominator to 8 and the numerator to 30. Now, you have two fractions, 30/8 and 3/8, with common denominators. Divide 30 by 3, you get 10. 10 books for the first part. Using this explanation you'll find that the new shelf can hold 14 books.