The First-Order Decomposition of Cyclopropane Has a Rate Constant of 6.7

The first-order decomposition of cyclopropane has a rate constant of 6.7 × 10^-4 s^-1. If the initial concentration of cyclopropane is 1.33 mol L^-1, what is the concentration of cyclopropane after 644 s?

A) 0.43 mol L^-1
B) 0.15 mol L^-1
C) 0.94 mol L^-1
D) 0.86 mol L^-1
E) 0.67 mol L^-1