Astudent creates a function to represent the cost of pencils available for purchase at the school store. the school charges 5 cents per pencil for up to 20 pencils. what is the domain of the function?
a.) all integers from 0 to 20
b.) all real numbers from 0 to 20
c.) all integer multiples of 5 from 5 to 100
d.) all real number multiples of 5 from 5 to 100