It took 3 hours or 180 minutes (12:30 to 3:30) to get to Marta's house, stay there, and come back. Since she stayed at the house for 90 minutes, we know the trip back and forth took 90 minutes (1.5h). They travel the distance twice at an average speed of 7.25 mi/h, as one trip of the same distance is 12 and the way back is 2.5. (12 + 2.5)/2 = 7.25. It took 1.5h to travel the distance twice at an average of 7.25 mi/h, so doing some math... (7.25 x 1.5)/2 = 5.4375 miles. Using fractions, you get 87/16 mi in improper fraction form and 5 7/16 mi in mixed numbers form.