Answer:
3 is the correct answer.
Explanation:
The slope of any line can be deyermined by using realation,
![m = (y2 - y1)/(x2 - x2)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/4ccgd8zm3ycivplir7oji3f6hz36bc8gtb.png)
i.e. the change in value of y per the change in value of x.
In this case, the slope is cost(y-axis) per item(x-axis)
so the answer is unit cost per item.