Where r is in decimal form. From the details given in the problem Principle P 8000 and R 9 or 009 expressed as a decimal. Principal rate of simple interest and amount problems.
So let us change the given time period in years.
In simple interest formula we use time period in years. In simple interest a sum of money doubles itself in 10 years. But the time period given in the question is in months. The Simple Interest Formula is given by.