Mai invested $7000 in a money-market fund that paid 6.2% simple interest . what was the value of her account at the end of 18 months?

The formula of simple interest is: I=PRT
Where:
I stands for Interest
P stands for Price (or Principle Amount)
R stands for Rate
T stands for Time (in years)
I=PRT
 =7000×0.062×1.5  
         (6.2%==0.062)
          (18 months=12 months and 6 months=1.5 year)   
 =$651
$7000+$651=$7651
By the end of 18 months, Mai has $7651 in her account

In this problem it decreased 20%