Answer:
The answer to you question is months 4 and 5
Step-by-step explanation:
To solve this problem get the slope of the different intervals
2-3 Months    m = (80 - 110) / (3 - 2)
               = -30 / 1
               = -30
3 - 4 Months   m = (50 - 80) / (4 - 1)
               = -30 / 1
               = -30
4 - 5 Months   m = (90 - 50) / (5 - 1)
                = 40 / 1
                = 40
5 -6 Months    m = (110- 90) / (6 - 5)
                = 20 / 1
               = 20
Conclusion
The greatest change was between the months 4 and 5