Equilibrium constant: Kp

Consider the equilibrium reaction: 2 NO2 (g) N2O4 (g)
A container initially holds a mixture of 2.0 atm of N2O4 and 1.0 atm of NO2. The system is allowed to equilibrate and it is noticed that the pressure of NO2 has increased by 0.3 atm. What is the Kp for this equilibrium?
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