FormulaWithUnits(), these answers won't produce the correct MathObjects when re-parsed.
You only need to use quotation marks around the answer if it is a formula that hasn't been parsed into a MathObject yet (e.g.,
Similarly, for your example
$Temp = NumberWithUnits("$g", "m/s");, there is no need to put
$gin quotation marks, in general.
Finally, note that the definition of
Terminalis missing the dollar sign (it should be
$Terminal = ...