Lucy needs to buy some organic apples, and her grocery store is having a sale on them. if she buys 3 or fewer pounds of apples, the price will be $1.50 per pound. if she buys more than 3 pounds of apples, the price is $1.10 per pound. what is the domain of the piecewise-defined function, where x represents the number of pounds of apples?
a) {x| x ≥ 0}
b) {x| x is a real number}
c) {x| 0 ≤ x ≤ 3}
d) {x| x ≥ 3}