Excel - steepest and least steep lines

Is there any way in Excel that I can get the steepest line and least steep line, given a linear graph?

If it's not possible to get these lines, is there a way I can (using Excel) calculate the gradient given a line.

Below, the graph I am working with.

enter image description here


Unfortunately, you have to write a VBA macro to do this. This functionality is not built in.

Note that in some cases, there is no solution to this problem. In your example, if the last point is at (100,0) instead of (100,81), then no line exists that can traverse all error boxes.