To find how many days it will take for the library to be sure it can run the event, we need to formulate the situation into an inequality.
Currently, there are 3 people signed up, and the library expects 2 more people to sign up each day. After \(d\) days, the number of people signed up can be represented as:
\[ 3 + 2d \]
For the event to run, at least 15 people need to sign up. Thus, we need the following inequality:
\[ 3 + 2d \geq 15 \]
This means that after \(d\) days, the total number of people signed up must be greater than or equal to 15.
So the correct response is:
2d + 3 ≥ 15, where d is the number of days.