documentclass[a4paper,11pt]{report}

usepackage{enumitem}

newlist{evenenumerate}{enumerate}{1}
setlist[evenenumerate]{label=Question theevenenumeratei.}
makeatletter

renewcommandtheevenenumeratei{@arabic{numexpr2*%
value{evenenumeratei}}}
%I broke this line to make it fit in this text area
makeatother

newcommand{evenquestions}{evenenumerate}
newcommand{question}{item}

begin{document}

noindent

In Exercises 1–6, bla bla.

begin{evenquestions}
    question foo 2
    \
    question foo 4
    \
    question foo 6
end{evenquestions}

noindent In Exercises 8-16, bla bla bla

begin{evenquestions}[resume]
    question foo 8
    \
    question foo 10
    \
    question foo 12
    \
    question foo 14
    \
    question foo 16
end{evenquestions}
end{document}