Algebraic expression for this the product of a number and 15

Create a real-life situation and create a system and show how it might be modeled algebraically with a system of equations (or inequalities) show all work include a few sentences explaining the situation, your variables of choice and what each represents, and how you would set it up and solve it algebraically. !

F(n + 1) = f(n) – 8. if f(1) = 100, what is f(6)?

What is always true about a positive integer raised to a negative odd power?