To determine when the library can be sure to run the event, we can set up an inequality based on the problem's parameters.
Currently, 3 people have signed up, and the library expects 2 more people to sign up each day. We want to know how many days, \(d\), it will take until the total number of sign-ups is at least 15.
The total number of people signed up after \(d\) days can be represented by the equation: \[ 3 + 2d \] We want this total to be at least 15: \[ 3 + 2d \geq 15 \]
Thus, the correct inequality to solve the problem is: \[ 2d + 3 \geq 15 \]
So the right response is: 2d + 3 ≥ 15, where d is the number of days.