Chemistry Question - Finding Weight Percentage?

When heated, MgCO3(s) decomposes to MgO(s) and CO2(g). Given 1.17g of a mixture of MgCO3 and MgO, 282mL of CO2(g) are collected over water at 15�C. The total pressure of gas in the collection flask is 750mmHg. What is the weight percentage of MgCO3 in the sample? (Vapor Pressure of water at 15�C is 12.8mmHg.)