If the rate is being reduced at 8.1% per year, it should take about 4 years for it to reach 30%. The exact answer is 3 years and 8 months. To find this, you need to divide the 30% by 8.1 which gives you roughly 3.7. Now, a year doesn't have 10 months, so we can't say its 7 months. What you need to do to solve this is use cross products. You set up the proportion like this.
7 x
--- = ---
10 12
You multiply the 7 and the 12 to get 84. Now we know the product of 10 and x is 84 as well. To find this, we divide 84 by 10 to give us 8.4. Rounded, this is 8 meaning you have 8 months. When you put all this together, your answer is 3 years and 8 months.
