Adam wants to ride her bicycle more than 80 miles this week, he has already ridden his bicycle 18 miles. Which inequality could be used to determine the mean number of miles, m, he would need to ride his bicycle each day for six more days to achieve his goal?

A. 6m + 18 < 80
B. 6m - 18 < 80
C. 6m + 18 > 80
D. 6m - 18 > 80