Can anyone help me with number 7 a b and c?

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

Consider u = {x|x is a negative real number}which is an empty set? o {x|x eu and x has a negative cube root}o {x|x eu and x has a negative square root}{x|x eu and x is equal to the product of a positive number and -1}{x|x eu and x is equal to the sum of one negative and one positive number?

5,678.321 what place value is the 1 in