[High School, AP Clac BC] Volume by Cross Section

Based on the three lines that are given in the question, I am having a hard time figuring out where exactly the volume by cross sections is needed to be taken. Because the ln graph never touches x=0, I am assuming that everything underneath the y-axis does not need to be considered in the calculations. Therefore my math is based on there being another restriction line of y=0. Is this a correct assumption or is there something that I am missing? Here is a link to my work. http://imgur.com/V5yhgFl