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.What is the value of the equilibrium constant for this system?

A) 0.5
B) 2
C) 20
D) 0.05
E) 5