Answer:
Well, it depends.
Explanation:
In the problem, it doesn't specify if the miles she runs is a positive integer or not, but I will assume that it is.
There are number of miles: 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, and 31.
So t = 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, and 31