The data for the conversion of A to B on heating the solid to 808C appear in the table. Assuming that the reaction follows Avrami kinetics, determine the rate of the reaction.

\begin{tabular}{|c|c|} \hline t, min & alfa \\ \hline 0 & 0 \\ \hline 10 & 0.076 \\ \hline 20 & 0.276 \\ \hline 30 & 0.538 \\ \hline 40 & 0.79 \\ \hline 50 & 0.988 \\ \hline \end{tabular}