A certain sum amounts to ₹798.60 after 3 years and ₹878.46 after 4 years. Find the interest rate and the sum.

In what time will ₹15625 amount to ₹17576 at 4% per annum compound interest?

Find the time (in years) in which ₹12500 will produce ₹3246.40 as compound interest at 8% per annum, interest compounded annually.

₹16000 invested at 10% p.a., compounded semi-annually, amounts to ₹18522. Find the time period of investment.