Let the time in hours after Marisol starts walking be t and so the time in hours after Mimi starts walking is (t-1) The distance walked by Marisol=speed*time=2t Distance walked by Mimi=3(t-1)
When they've reached school they've all walked the same distance so: 3(t-1)=2t 3t-3=2t 3t-2t=3 t=3 Thus the distance from the mall to their school is 2t=2*3=6 miles