Final answer:
To find the average miles Sandy has run each month, divide the total miles by the number of months. In this case, she has run 4,272 miles over 12 years, which is equivalent to 30 miles/month.
Step-by-step explanation:
To find out how many miles Sandy has run each month on average, we need to divide the total miles she has run by the number of months. In this case, Sandy has run 4,272 miles over 12 years, which is equivalent to 144 months (12 years x 12 months/year). So, the average miles she has run each month is 4,272 miles / 144 months = 29.67 miles/month, which rounds to the nearest whole number as 30 miles/month.
Therefore, the correct answer is 30 miles (option a).