how to convert this close/last from string to float under a new column close_last

\begin{tabular}{rr} Close/Last & Volume \\ \hline$98.15 & 56339170 \\ $101.16 & 48053880 \\ $99.7 & 56202900 \\ $99.54 & 52841460 \\ $97.61 & 52740130 \\ \hline & \\ $151.358 & 100785760 \\ $144.827 & 64243560 \\ $150.1975 & 66128240 \\ $152.6015 & 63604100 \\ $154.6525 & 64032500 \end{tabular}