How to make a report that shows a "y" value when an "x" value is input.

How to make a report that shows a "y" value when an "x" value is input.

So basically i want to be able to have a list of "height" values that the application user can choose from (from a drop down menu or something similar) and a corresponding "flow" value that will result from each individual height value that is input into the application. Any help would be greatly appreciated!! Thanks!