The graph shows the cost of a lunch in a school’s cafeteria since school started.

A graph titled Cost of a Lunch in a School's Cafeteria has Days since school started on the x-axis and cost of lunch (dollars) on the y-axis. A horizontal line is at y = 2.5.

Which is correct about the graph’s slope?
Its slope is positive.
Its slope is negative.
Its slope is zero.
It has no slope.

Since there is a horizontal line at y = 2.5, the graph has no slope. The cost of lunch remains constant over time.

The graph represents a horizontal line at y = 2.5. A horizontal line has a slope of zero. Therefore, the correct answer is: Its slope is zero.