Which relation is a function? NEED HELP ASAP PLS

{(0, 2), (0, 4), (0, 6), (0, 8)}

{(1, 2), (2, 3), (3, 4), (4, 5)}

{(1, 2), (2, 1), (1, 3), (3, 1)}

{(1, 2), (3, 4), (5, 6), (1, 8)}

Joel wants to buy a new tablet computer fram a store having a 20% off sale on all tablets. the tablet he wants has an original cost of $190. he also wants to make sure he has enough money to pay the 5% sales tax. part one joel uses the incorect expression 0.95(190)(0.8) to calculate that the tablet will cost him a total of $144.40. describe his error and write the correct expression part two how much will joel pay for the tablet show your work if you answer this question correctly you will receive a prize of 99 points good luck