Suppose that you decide to participate in a charity walkathon to raise money for your cause. Some people decide to donate a fixed amount, while others donate a little money for every mile you walk. Before the event starts, you raised $25, and you have been pledged $1.50 for each mile you walk. The function defined by d(m)=1.5m+25 can be used to relate the miles you walk, m, and the amount of money donated to you in dollars, d(m). While you were walking, you lost track of the number of miles you had walked. At the end of the event, an organizer tells you that you raised $40 through your walk. How many miles did you walk?