(New User) How to project a 3D histogram along Y-axis

Hi, I was just wondering how to take a graphical cut (“CUTG”) from a 3D histogram and project it along the y-axis?


This is what I’m trying to do:
-I have a 3D histogram that is in the 2D view with a regular xy-axis.
-I need to make a fairly small cut in the histogram that is parallel to the y-axis.
-Then I need to project the cut to the y-axis.
Hopefully this helps. Thanks. (I am using ROOT version 5.10)