from 0 hr to 2 hr in the graph, the height of the snow after a snowfall is changed 0 to 2 inches of snow,
so this relation between the 0 to 2 hr is a proportional relationship. and the rate of snowfall between these hours is 1 inch of snow per hour.
From 2 to 5 hours the height of the snow is constant, so there is now snowfall in between 2 to 5. so the rate of snowfall is 0 in between 2 to 5 hrs
from 5 to 6 hr,
the height of snow increases proportionally to the time. it means there is a proportional relation between 5 to 6 hr
so the rate of snow 1-inch per hour