I'm struggling so much I need help. Please answer moderately descriptive as that is required of me.

For the equations below which statement is true ?

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

The ideal weight of a nickel is 0.176 ounce. to check that there are 40 nickels in a roll, a bank weighs the roll and allows for an error of 0.015 ounce in total weight