Find the principal which will amount to ₹ 4,000 in 4 years at 6.25% per annum.

At what rate per cent per annum will ₹ 630 produce an interest of ₹ 126 in 4 years?

Find the rates of interest per year, if the interest charged for 8 months be 0.06 times of the money borrowed.

In how many years will ₹ 950 produce ₹ 399 as simple interest at 7% ?