Choose two points on the line.
Count the number of units it will require to go from one point to another. The number of units left or right is the run. The number of units up or down is the rise. Movement left or down on the grid is a negative number. Movement right or up is a positive number. For example, if travel from point A to point B requires moving three units to the left, the line has a run of -3. If the same line requires moving three units up, the line has a rise of 3.
Divide the rise over the run. For example, if the rise is 3 and the run is -3, the result is -1. This result is the slope.
Express the equation slope is equal to rise divided by run.
Modify the equation to solve for rise instead of slope. To do this, multiply the slope by the run.
Solve the equation. For example, if the slope of the line is -1 and its run is -3, multiply -1 by -3. The result is the rise. In the example, the rise is equal to 3.