What table shows a constant rate of change
A; hours : 2 , 7 , 14
earnings : 40 , 60 , 80
B; hours : 2 , 7 , 14
earnings : 40 , 140 , 280
C ;hours: 2 , 7 , 14
earnings : 40 , 70 , 140
A; hours : 2 , 7 , 14
earnings : 40 , 60 , 80
B; hours : 2 , 7 , 14
earnings : 40 , 140 , 280
C ;hours: 2 , 7 , 14
earnings : 40 , 70 , 140