In the Gas Phase at 500 $\degree$ C, Cyclopropane Reacts to Form Propene in a First-Order Reaction

In the gas phase at 500. $\degree$ C, cyclopropane reacts to form propene in a first-order reaction. The figure below shows the concentration of cyclopropane plotted versus time. Use the graph to calculate approximate values of
A) the rate of the reaction, 600. seconds after the start.
B) the half-life of the reaction, t_1/2.