Check the data type of your cell. If it's not numeric (whether that's currency, accounting, etc.) in the Format Cells, Number tab, formulas quite literally do not compute. They amount to text.
You must have a numeric cell format for formulas, even ones using two constants as you've given here, to actually compute numeric values.
My guess is that the cell in question is set to general or text format under the Number tab.
Brian - Windows 10, 64-Bit, Version 21H1, Build 19043
It is the function of creative men to perceive the relations between thoughts, or things, or forms of expression that may seem utterly different, and to be able to combine them into some new forms--the power to connect the seemingly unconnected.
~ William Plomer