What is total pressure inside the flask before the reaction

A 1.500L flask is filled with a mixture of 1.20g H2 and 8.40g O2 at 25 degrees C.The mixture is ignited and hydrogen and oxygen combine to form water.a. What is total pressure inside the flask before the reaction? (report your answer in atmospheres.)b. What is the total pressure after the reaction once the flask is returned to 25 degrees C? (Vapor pressure of water at 25 C is 23.8 mm Hg)