Zach plans to save $25 a week to purchase a new bike. The function f(x)=250-25x models the amount of money Zach will need to purchase the bike x weeks after he starts saving. Which is the most appropriate domain for the function? a) All integers less than or equal to 10
b) All integers greater than or equal to 10
c) All non-negative integers less than or equal to 10
d) All non-negative integers greater than or equal to 10