To produce an annual income of Rs. 800 from a 8% stock at 90, the amount of stock needed is:
Since face value is not given, take it as Rs.100.
As it is an 8% stock, income [dividend] per stock = Rs.8
ie, For an income of Rs.8,amount of stock needed = Rs.100
For an income of Rs.800, amount of stock needed = $\dfrac{100 \times 800}{8}$ = 10000