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.

$$\begin{array} { l | l | l } \hline & { 2018 } & { 2017 } \\\text { Sales } & \$ 720,000 & \$ 607,500 \\\hline \text { Gross profit } & 270,000 & 224,800 \\\hline \text { Income before taxes } & 79,200 & 78,700 \\\hline \text { Net income } & 51,200 & 51,700\\\hline & & \\\hline & { 2018 } & { 2017 } \\ \hline \text { Liabilities } & \$ 493,500 & \$ 452,500 \\\hline \text { Common stock (\$12 par) } & 180,000 & 180,000 \\\hline \text { Contributed capital in excess of par } & 135,000 & 135,000 \\\hline \text { Retained earnings } & \underline{204,000} & 177,300 \\\hline \text { Total liabilities and equity } & \$ 1,012,500 & \$ 944,800\\\hline\end{array}$$