Slope of a line is equal to
![(y2-y1)/(x2-x1)](https://img.qammunity.org/2023/formulas/mathematics/middle-school/sjgz1fvowydouk6sw5i02b2w4cz5te0z47.png)
In this case, its not necessary because as the x value increases (time),
the y value does not change. The slope is 0.
But, to use the slope of a line formula you would just take to points
y2 is a y value further along and y1 is a y value before. Same with x.