It REALLY helps to write complete definitions.
Distance is in Miles
Time is in Hours
X = Jogging Rate in mph -- This would be a little better.
X mph = Jogging Rate -- I would prefer this
X mph + 9 mph = Car Driving Rate
Now, WRITE IT DOWN!!
Distance = Rate * Time
8 Mile = X mph * Time
16 Mile = (X mph + 9 mph) * Time
We know already that "Time" is the same in each.
Now, what on earth is that 1/8 mph business? First, it takes 64 hours to get 8 miles at this speed. Second, the units aren't even mph. What are they? It is all very confusing. Never do that. Third, you're going to get a lot more than 16 miles at 9.125 mph for 64 hours. You do need to make sure your answers make sense.