To find out how long it will take Lena to bike 3 miles to the comic book store, we first need to determine her biking speed in miles per minute.
Lena can bike 12 miles in 1 hour. Since there are 60 minutes in an hour, we can calculate her speed in miles per minute as follows:
\[ \text{Speed} = \frac{12 \text{ miles}}{60 \text{ minutes}} = 0.2 \text{ miles per minute} \]
Next, we need to find out how long it takes her to bike 3 miles. We can do this using the formula:
\[ \text{Time} = \frac{\text{Distance}}{\text{Speed}} \]
Substituting in the values:
\[ \text{Time} = \frac{3 \text{ miles}}{0.2 \text{ miles per minute}} = 15 \text{ minutes} \]
Thus, it will take Lena 15 minutes to bike to the comic book store.