Simple Interest - General Questions

At 10% per annum simple interest, what principal yields Rs. 1,000 as interest in 5 years?

What is the simple interest on Rs. 12,000 at 12% per annum for 6 years?

At 8% per annum simple interest, what principal yields Rs. 4,800 as interest in 5 years?

What is the simple interest on Rs. 5,500 at 12% per annum for 4 years?

In how many years will a sum of money double itself at 4% per annum simple interest?