A businessman agrees to pay a debt of Tk. 20,000 with 10% compound interest. After how many years he will pay total amount of Tk. 51,874.85.

In a class, if 4 students sit in each bench, 3 benches remain empty. But if 3 students sit in each bench, 6 students do not get any seat. Find the total number of students. 

The ratio of prices of two houses was 16:23. Two years later when the prices of the first had risen by 10% and that of second by Tk. 477, the ratio of their prices become 11:20. Find the original prices of the two houses.