3. For every book that Emmitt reads, he gets twenty points of extra credit from his history teacher. In this situation, what does the dependent variable represent? the type of books Emmitt reads The amount of extra credit Emmitt receives from his history teacher. the number of books Emmitt reads

Step 1 ：The dependent variable is the one that is affected by the independent variable. In this case, the number of books Emmitt reads is the independent variable, because it can be changed freely. The amount of extra credit Emmitt receives from his history teacher is the dependent variable, because it depends on the number of books Emmitt reads. The type of books Emmitt reads is not relevant in this situation.

Step 2 ：Final Answer: \(\boxed{\text{The amount of extra credit Emmitt receives from his history teacher.}}\)