Hi,
no it should not be shown as you say. Note that
$m$ has no units. You have the value of 0.1 and you subtract it from 1, which has no units. that means the the second term of
$H_v$ does not have any units either, just as the
$(1-m)$ expression in the first term. The thinh his that the first term is multiplied by
$t$, which does have units. That means that your equation is inconsistent and should not simplify as you say.
It would also be useful if you typed in the equations instead of using a screenshot.
pille = Quantity[19.0, "Gigajoules"/"MetricTons"];
Subscript[Hnew, v][m_, t_] := t*(1 - m) - Quantity[2.442, "Gigajoules"/"MetricTons"] * m
Subscript[Hnew, v][0.1, pille]
gives the result that you expect.
Cheers,
Marco
