You need to remember that if a sequence of terms has a linear growth, then the difference between any two successive terms is a constant and the sequence is an arithmetic sequence.
If the difference is a negative term, then the sequence is equivalent to a decay and if the difference is a positive term then the sequence is equivalent to a growth.
The arithmetic sequence is the best function that helps you to analyze the growth or decay of simple interest, while the geometric sequence helps you to analyze the compound interest.
The simple interest expresses the money that you will get by investing a principal amount of money. You can evaluate the simple interest by adding a fixed percentage of the principal amount of money.