I need to figure out how to find the solution before tomorrow...?

The stoichiometry of the reaction tells you that you will get 1 mole of O2 (g) for every 3 moles of UO2Cl2 (g) that form. Since partial pressure is proportional to moles, you can just divide the equilibrium partial pressure of UO2Cl2 (g) by 3 to find the partial pressure of O2 (g) at equilibrium.