**Answer:**

The correct answer is B. {0, 20, 40, 60, 80, 100, 120}

**Step-by-step explanation:**

**1. Let's check all the information given to answer this question correctly:**

**Rate of each piano lesson Blake gives = US$ 20**

**Blake can give between 0 and 6 lessons every evening**

**Earnings = Number of lessons * Rate of each lesson**

**2. What is the range of this relation?**

**Let's recall that the domain of a relation is the set of all values for which the relation is defined, and the range of the relation is the set of all values that the relation takes.**

**It means that the domain of the relation in this case is the number of lessons that Blake can give every evening:**

**{0, 1, 2, 3, 4, 5, 6}**

**And the range of this relation is the amount Blake earns in an evening depending on the number of lessons he gives:**

**{0, 20, 40, 60, 80, 100, 120}**

**The correct answer is B. {0, 20, 40, 60, 80, 100, 120}**

Let b(t) be the number of unread books remaining on Alex's bookshelf after reading consistently for t months.