This is a two state economy with two securities. Calculate the risk-free rate

\begin{tabular}{|c|c|c|c|} \hline & Boom State 1 Probability =0.4 & Slump State 2 Probability =0.6 & Price \\ \hline Security S & $40 & $15 & $20 \\ \hline Security T & $10 & $35 & $20 \\ \hline \end{tabular}