Assume that common shareholders' equity at the end of $2018$ was equal to the amount for $2019.$ Why is the return on common shareholders' equity different from the return on assets? Why does the difference between these two ratios change?

$\backslash$table$[[$Return on common shareholders' equity,$10\mathrm{.}7\%,9\mathrm{.}0\%,7\mathrm{.}5\%$