1 Which relation is not a function?

1) {(1,5),(2,6),(3,6),(4,7)}

2) {(4,7),(2,1),(−3,6),(3,4)}

3) {(−1,6),(1,3),(2,5),(1,7)}

4) {(−1,2),(0,5),(5,0),(2,−1)}

One cell phone plan charges $20 per month plus $0.15 per minute used. a second cell phone plan charges $35 per month plus $0.10 per minute used. write and solve an equation to find the number of minutes you must talk to have the same cost for both calling plans.