N molecules, each of mass m of gas A, and 2N molecules, each of mass 2m of gas  B, are contained in the same vessel which is maintained at a temperature T. The  mean square of the velocity of the molecules of B type is denoted by vB2  and the  mean square of the x-component of the velocity of A type is denoted by vA2 . The  ratio  vB2vA2=N3 . Find N.