A Chemical Equilibrium 2 A $\leftrightarrows$ B Has a Forward Rate Constant,k_f = 10 M ^-1

A chemical equilibrium 2 A $\leftrightarrows$ B has a forward rate constant,k_f = 10 M ^-1 s^-1,and a reverse rate constant,k_r = 5 s^-1.If the system has a concentration of [A] = 0.10 M at equilibrium,what is the concentration of B at equilibrium?

A) 20
B) 2
C) 0.2
D) 0.02
E) 200