13.The value of machine depreciates every year at the rate at108 on its value at the beginning of that year. If the present value of the machine is Rs. 729, its worth 3 years ago was:

14. The difference between the compound interest and the simple in interest on a certain sum at 5% per annum for 2 years is Rs. 1.50. The sum is:

15. A tree increases annually by 1/8 th of its height, By how much will at increase after 2 years, it stand-today 64cm high?