Read the "Add Mixed Numbers" section, which explains the two methods for adding mixed numbers. Do examples 4.83 and 4.84 using the method of adding the whole numbers and fractions separately. Then, do example 4.85 using the method of converting mixed numbers to improper fractions.
Then, read the "Subtract Mixed Numbers with a Common Denominator" section, which describes both methods for subtracting mixed numbers with common denominators. Do example 4.90 using the whole numbers and fraction method, and do example 4.91 using the improper fraction method.