Chapter 4 - An Introduction to Functions - 4-3 Patterns and Nonlinear Functions - Practice and Problem-Solving Exercises - Page 250: 17

independent variable :r , dependent variable : V , because the radius determines the volume of a sphere .

from the question , we could find that variables are V and r . And from the definition of independent variable , r could change constantly and V couldn't. V is affected by r , so we could get the result.