Consider the Following Reaction (Assume an Ideal Gas Mixture)

Consider the following reaction (assume an ideal gas mixture) .2NOBr(g) 2NO(g) + Br₂(g)
A 3) 0-L vessel was initially filled with pure NOBr, at a pressure of 3.9 atm, at 310K.After equilibrium was established, the partial pressure of NOBr was 2.1 atm. What is K_p for the reaction?

A) 0.66
B) 0.22
C) 1.32
D) 1.54
E) 1.1