6000 becomes7200 in 4 years. If the rate becomes 1.5 time of itself, the amount of

Rs . 6000 becomes Rs, 7200 in 4 years. If the rate becomes 1.5 times of itself, the amount of the same principal in 5 years will be

Rs 6000 becomes Rs 7200 in 4 years at a certain rate of simple interest. If the rate becomes 1.5 times of itself, the amount of the same principal in 5 years will be (a) Rs 8000 (b) Rs 8250 (c) Rs 9000 (d) Rs 9250

If certain sum becomes 3 times itself in 4 years at compound interest, in how many years will the sum become 81 times itself at the same rate of interest?