Let "r" be the slower rate, in miles per hour. Then the faster rate is (r+20) mph. The distance is 12r miles on the way to the mountains. The distance is 8*(r+20) on the way back. The distances are the same, so 12r = 8*(r+20) ====> 12r = 8r + 160 ====> 4r = 160 ====> r == 40. Answer. The slower rate is 40 mph, and the one-way distance is 12*40 = 480 miles.