Please answer it.

Please answer it. 9. An element X is found to combine with oxygen to form X40G. If 8.4 gm of this element combines with 6.4 gm of oxygen, then calculate the atomic weight of X.

Dear student,

As per the given formula : 6 x 16 gm of O combines with 4 x MW_X gm of X
Now it is given that 6.4 gm of O combines with 8.4 gm of X
     Then    :  6 x 16 gm of O combines with $\frac{8.4}{6.4} \times 6\times 16$  =  4 x MW
                             Therefore Molecular weight of X = 31.5 gm /mol
  Regards