Answer: The ratio of the number of miles Mariana has left to drive to the total number of miles on her trip can be calculated as follows:
Miles left to drive = Total miles - Miles driven so far
Miles left to drive = 36 miles - 13 miles
Miles left to drive = 23 miles
Ratio = Miles left to drive / Total miles
Ratio = 23 miles / 36 miles
Simplifying the ratio by dividing both the numerator and the denominator by their greatest common divisor, which is 1:
Ratio = 23/36
So, the ratio of the number of miles Mariana has left to drive to the total number of miles on her trip is 23/36.