Between 2010 and 2013 the rate of change is:
[210 - 120] / [2013 - 2010] = 90/3 = 30 (Well done!)
Between 2013 and 2019 the rate of change is:
[120 - 210] / [2019 - 2013] = - 90/ 6 = -15 (WEll done! again!)
Between 2010 and 2019 the rate of change is:
[120 - 120] / [2019 - 2010] = 0/9 = 0 (Perfect again!)
Well done!
I am glad you got the concept perfect!
Your answers are right on the spot!