Answer:
7 . . . . . inches per week
Explanation:
The average rate of change of height is ...
... (change in height)/(change in time)
The height changes from 41 inches to 83 inches when the time changes from 3 weeks to 9 weeks. Then the rate of change is ...
... (83 -41) inches/((9 -3) weeks) = (42/6) inches/week = 7 inches/week
It seems likely that the required answer will just be a number: 7.