The ratio of the monthly incomes of X and Y is 5 : 4 and that of their monthly expenditures is 9 : 7. If the income of Y is equal to the expenditure of X, then what is the ratio of the saving of X and Y?

\[\begin{array}{*{20}{c}} {}&{{\text{X}}\,\,\,\,\,:\,\,\,\,\,{\text{Y}}} \\ {{\text{Income}} \to }&{{5_{ \times 9}}\,\,\,:\,\,\,{4_{ \times 9}}} \\ {{\text{Expenditure}} \to }&{{9_{ \times 4}}\,\,\,:\,\,\,{7_{ \times 4}}} \\ {{\text{Saving}} \to }&{\overline {\underline {\,\,9\,\,\,\,\,\,:\,\,\,\,\,\,8\,\,} } } \end{array}\]
Y's income = X's Expenditure
Saving = 9 : 8