David opened a recurring deposit account in a bank and deposited ₹300 per month for two years. If he received ₹7,725 at the time of maturity, find the rate of interest per annum.

Preeti has a recurring deposit account of ₹1,000 per month at 10% per annum. If she gets ₹5,550 as interest at the time of maturity, find the total time for which the account was held.

Mr. Sonu has a recurring deposit account and deposits ₹750 per month for 2 years. If he gets ₹19,125 at the time of maturity, find the rate of interest.

Salman deposits ₹1,000 every month in a recurring deposit account for 2 years. If he receives ₹26,000 on maturity, find:

(i) the total interest Salman earns.

(ii) the rate of interest.