To find out how many miles Alison has driven this month, we first need to determine her average miles driven per day.
Last month, Alison drove 230.4 miles over 18 days.
To find her average daily mileage: \[ \text{Average miles per day} = \frac{\text{Total miles}}{\text{Number of days}} = \frac{230.4 \text{ miles}}{18 \text{ days}} \approx 12.8 \text{ miles per day} \]
Now, if she has driven to work for 21 days this month, we can calculate the total miles driven this month using the average we just found: \[ \text{Total miles this month} = \text{Average miles per day} \times \text{Number of days} = 12.8 \text{ miles/day} \times 21 \text{ days} = 268.8 \text{ miles} \]
Therefore, Alison has driven 268.8 miles this month.