Which set is a function?

a)
{(0,3), (3,0), (0,4), (4,0)}

b)
{(0,2), (2,0), (4,6), (6,4)}

c)
{(2,6), (3,6), (4,6), (2,0)}

d)
{(6,2), (2,0), (4,6), (6,4)}

What is the prime factorization of 23 ?me with this question

At the electronics store you have a coupon for 20% off up to 2 cds you buy for cds with the original cost of $10.99 each the sales tax is 5% what is the total cost of your purchase

When you have 25 numbers, and jake picks 3 random numbers and puts them back, what is the chance bob has of picking those 3 numbers when he picks 6 random numbers (without putting them back)? explain.