When I use this formula, =-, I get the wrong answer. If B7=100 and B8=40, the answer should be 60, but the result I get is -40. Is this possible, and if so, what’s the syntax? Thanks!
Your syntax is correct. But the result shows that your “100” in B7 isn’t recognized as number. Does it contain e.g. letter “O” instead of a zero?
Another possibility is if you have an error in formula (highly improbable if you used mouse clicks to select cells when entered formula), e.g. use letter similar to B (in Russia e.g., we have a letter В that looks identically, but is a different Cyrillic letter). But then it would give you **Error in expression** and replace your wrong <B7> with <?> upon formula entry finished.
… is it possible to subtract [the value stored in] one cell from [the value stored in] another cell?
Yes.
See the documentation and read the chapter on tables and number recognition; or search Help.