Simple Interest - General Questions

A sum of money amounts to Rs. 12,040 in 4 years and to Rs. 12,900 in 5 years at simple interest. What is the sum?

In how many years will a sum of money double itself at 10% per annum simple interest?

What is the simple interest on Rs. 19,000 at 10% per annum for 4 years?

In how many years will a sum of money double itself at 12.5% per annum simple interest?

At 5% per annum simple interest, what principal yields Rs. 400 as interest in 2 years?