Determining missing items in return on investment computations

One item is omitted from each of the following computations of the return on investment:

Return on Investment$=$Profit MarginxInvestment Turnover$24\%=10\%$x$($a$)($b$)=28\%$x$0\mathrm{.}7521\%=($c$)$x$1\mathrm{.}5012\%=20\%$x$($d$)($e$)=0\mathrm{.}15$x$2\mathrm{.}20$

Determine the missing items, identifying each by the appropriate letter. Round investment turnover amounts to two decimal places.