Idon't get this and i'm really lost

What is the slope of the line shown below?

Neoli is a nurse who works each day from 8: 00 am to 4: 00 pm at the blood collection centre. she takes 45 minutes for her lunch break. on average, it takes neoli 15 minutes to collect each sample and record the patient's details. on average, how many patients can neoli see each day?

How do i i solve this equation? -18 = x/3 + 3