'David and his wife each receives an 8 percent annual rise. If David receives a raise of Rs. 800

"David and his wife each receives an 8 percent annual rise. If David
receives a raise of Rs. 800 and his wife receives a raise of Rs. 840, what is
the difference between their annual incomes after their raises?
`R s .40`
b. `R s .500`
c. `R s .460`
d. `R s .540`"