States Of Matter

4 g of an ideal gas $A$ (molar mass $=M_A$ ) present in a vessel of volume $V$ litre exerted a pressure of 5 atm at 300 K . When 16 g of another ideal gas $B$(molar mass $=M_B$ ) was introduced into this vessel at the same temperature, its pressure increased to 10 atm . What is the correct relationship between $M_A$ and $M_B$ ?