Creating multiple lines under same label in legend of ArcGIS Desktop?

This can be done with a bit of trial-and-error in the Legend settings.

In your Layer Properties Symbology tab, right-click on each symbol category and select Edit Description and enter the text you want on the second line eg (-102.12 - 17.92) and remove this text from the symbol label.

Second create your Legend. Once it's created double-click on it to open Legend Properties (this is because not all properties are available during Legend creation).

In the Legend Properties Items tab select Style at the bottom of the left-hand column, and select the style that most closely matches what you want to see (although there doesn't appear to be one that specifically matches your requirements - I chose Horizontal Single Symbol Description Only) then click the Properties button (don't press OK just yet)

In the Legend Item General tab make sure that both Show Labels and Show Descriptions are checked (I had to check on Show Labels) and click the Label Symbol button

In Symbol Selector click Edit Symbol, and then in Editor set the Y Offset to 5, then OK OK back to Legend Item again. Click on Description Symbol button then Edit Symbol again. This time set Y Offset to -5 and then this is where the trial-and-error comes into play. Set the X Offset to around -100 then OK, OK, OK, OK back to Legend Properties.

In Legend Properties click on the Layouts tab. Change the Text Gap to 0.00pt and the Vertical Patch Gap to 10.00pt and hit OK to save your Legend settings.

This should give a Legend that looks something like this (I've done this on a point layer so the symbols don't match, but the text on the legend is what you're after anyway)

You may need to adjust the X Offset settings up or down slightly depending on your font size and how far left or right you need your second line to move into position.

This may not be as quick to set up as converting to graphics, but one it's done you can make changes to your layer such as symbology or label/description and the legend will still automatically update with those changes.

To make changes in the legend, first you will have to enable editing, right click the legend -> convert to graphics , then select the labels you want to edit and right click -> ungroup.

Now you can manually move them around as much as you want and edit any individual parts, just move the lines with the text under the label. When you are satisfied with what you have, select all of them again , right click -> group, save edits and you are done.

Once you convert the legend to graphics you can no longer automatically update it, any changes you want to make to it will have to manual, or you will have to add a new legend.