Comparative Calendar Year Financial Data for a Company Are Shown

Comparative calendar year financial data for a company are shown below. Calculate the following ratios for 2018:
(a) return on total assets
(b) return on common stockholders' equity.
$\begin{array}{c}\begin{array}{|l|}\hline \\\hline \text {Sales}\\\hline \text {Gross profit}\\\hline \text {Income before taxes}\\\hline \text {Net income}\\\hline \\\hline \\\hline \\\hline \text {Liabilities}\\\hline \text {Common stock (\$12 par)}\\\hline \text {Contributed capital in excess of par}\\\hline \text {Retained earnings}\\\hline \text {Total liabilities and equity}\\\hline \end{array}\begin{array}{l|}\hline \underline{2018}\\\hline \underline{\$720,000} \\\hline \$ 270,000 \\\hline 79,200 \\\hline 51,200 \\\hline \\\hline \text { December } 31, \\\hline 2018 \\\hline \$ 493,500 \\\hline 180,000 \\\hline 135,000 \\\hline 204,000 \\\hline \$ 1,012,500 \\\hline\end{array}\begin{array}{l|}\hline \underline{2017}\\\hline\$ 607,500 \\\hline 224,800 \\\hline 78,700 \\\hline 51,700 \\\hline\\\hline \text { December } 31 \\\hline 2017\\\hline \$ 452,500 \\\hline 180,000 \\\hline 135,000 \\\hline 177,300 \\\hline \$ 944,800 \\\hline\end{array}\end{array}$