The Initial Concentration of a Reactant in a First-Order Reaction

The initial concentration of a reactant in a first-order reaction is 0.620 M. What will be its concentration after 3 half-lives have passed?

A) 0.0865 M
B) 0.0775 M
C) 0.310 M
D) 0.207 M
E) 0.103 M