A sum of money, lent out at simple interest, doubles itself in 8 years. Find:

(i) the rate of interest.

(ii) in how many years will the sum become triple (three times) of itself at the same rate percent?

What sum of money lent at 6.5% per annum will produce the same interest in 4 years as ₹ 7,500 produce in 6 years at 5% per annum?

A certain sum amounts to ₹ 3,825 in 4 years and to ₹ 4,050 in 6 years. Find the rate percent and the sum.