Answer: The number of miles would be no more than 350 miles.
Explanation:
Let the number of days be 'd'.
Let number of miles be 'm'.
Cost of each day = $75
Cost of each mile = $0.50
Total amount must be no more than $400.
According to question, it becomes,

Since the number of days = 3
So, we put the value of days in the above equation:

Hence, the number of miles would be no more than 350 miles.