[tex] \huge \boxed{\mathfrak{Question} \downarrow}[/tex]
[tex] \large \boxed{\mathfrak{Answer \: with \: Explanation} \downarrow}[/tex]
Given,
Let's solve it now :-
[tex] \sf \: c - 5d \\ \\ \sf \: Substitute \: the \: values \: of \: c \: and \: d \\ \\ \sf c - 5d \\ \rightarrow \sf(21) - 5(4) \\ \sf \rightarrow21 - 20 \\ = \boxed{\boxed{\bf \: 1}}[/tex]