Greg ran 12 miles a day on 18 different days last month. How many miles did he run?

To find out how many miles Greg ran, you can multiply the number of miles he runs each day by the number of days he ran:

\[ 12 \text{ miles/day} \times 18 \text{ days} = 216 \text{ miles} \]

So, Greg ran 216 miles last month.