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)}

Element x decays radioactively with a half life of 8 minutes. if there are 450 grams of element x, how long, to the nearest tenth of a minute, would it take the element to decay to 37 grams?

It took alice 5 5/6 hours to drive to her grandparents' house for . on the way home, she ran into traffic and it took her 7 3/8 hours. how much longer did the return trip take? write your answer as a proper fraction or mixed number in simplest form. the trip home took __hours longer. ?

Helll ! 1,400 tons of wheat of two different varieties was delivered to the silo. when processing one variety, there was 2% of waste and 3% during the processing of the second variety of wheat. after the processing, the amount of remaining wheat was 1,364 tons. how many tons of each variety of wheat was delivered to the silo?