This graph shows how the total length Tori has knit depends on the number of nights she has spent knitting.
Total length knit
100
90
80
70
60
Length knit centimeters)
50
40
30
20
10
Х
0
80
90 100
10 20 30 40 50 60 70
Nights
What is the rate of change?
Write your answer as a decimal or integer.