A Chemical Equilibrium 2 A B

A chemical equilibrium 2 A B
Has a forward rate constant, k_f = 10 M ^-1s^-1, and a reverse rate constant, k_r = 5.0 s^-1. What is the value of the equilibrium constant for this system?

A) 0.5
B) 2.0
C) 20
D) 0.050
E) 5.0