Simple Interest - General Questions

A sum of money amounts to Rs. 3,720 in 4 years and to Rs. 3,875 in 5 years at simple interest. What is the sum?

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

What is the simple interest on Rs. 18,000 at 15% per annum for 4 years?

At 10% per annum simple interest, what principal yields Rs. 7,000 as interest in 5 years?

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