To find the number of days until the library can be sure to run the event, we can set up the following inequality based on the given information:
- Current sign-ups: 3 people
- Expected daily sign-ups: 2 people per day
- Minimum required sign-ups: 15 people
Let \( d \) represent the number of days until the event.
The total number of people signed up after \( d \) days will be: \[ 3 + 2d \]
We need this total to be at least 15: \[ 3 + 2d \geq 15 \]
Thus, the correct inequality is: \[ 2d + 3 \geq 15 \]
This is the appropriate choice.