Having trouble adding

I was just trying out the equation in a custom field but I dont seem to be able to do it.
I have set up 2 custom fields in assets Depreciation and tax, then I have set up a 3rd custom field call answer…
I went into an asset and put 50 in depreciation and 50 in Tax and in the 3rd I put
< div >{{ custom_fields["Depreciation"] | plus: custom_fields["Tax"] }}</ div > which I copied off something lubos put in one of the Topics
then I go update and there is nothing there.
am I doing it right?

You don’t put the Liquid code into the custom field. You put it in a custom theme. Read the Guide again.

Oh whoops sorry I can not do what I wanted to do then never mind I keep trying all the new things.
I did not see a guide for this I only read it on the forum. and thought they were talking about custom fields.

The topic and Guide are very similar. Both discuss performing calculations on content of custom fields in custom themes.