documentclass{article}
usepackage[margin={1.25in,1.1in}]{geometry}
usepackage{mathtools,enumitem,lipsum}

newlist{exercises}{enumerate}{1}
setlist[exercises]{label=textbf{thesection-arabic*.;},align=right,leftmargin=0pt,itemsep=15pt}

newlist{subparts}{enumerate}{2}
setlist[subparts]{label=(roman*),align=left,widest=i}


begin{document}

section{Testing section}

begin{exercises}
%
item lipsum[1]

item
begin{subparts}
item lipsum[2]
item lipsum[3]
end{subparts}

item

end{exercises}

end{document}