How to control Music vs SFX vol using Master Mixer

I created several Audio Sources in my 3d game and they are working fine. Now I would like to present the user (at the Main Game Menu) with the traditional volume sliders to adjust Music vs SFX.

I carefully assigned my Audio Sources (in 3d editor) to Master Mixer Music or Master Mixer SFX, as appropriate. I also installed (prefabbed) sliders for SFX and Music vol. Now I am trying to find out the essential secret: how do I actually make the slider adjust the Master-Music (or Master-SFX) volume?

I have been searching for some sample code, but so far everything I'm finding refers to mixers created by the game author. These mixers, as far as I know, pre-exist in Unity 5. If anyone has sample code for tying a slider to either of the Master mix volumes, I'd be very grateful.