Jon planted a plant. When the plant grew to $4\,cm$ tall he decided to start to measure how much the plant grew each week.
Here are Jon's measurements:
Week $0$: $\;\;4\,cm$
Week $1$: $\;\;6\,cm$
Week $2$: $10\,cm$
Week $3$: $10\,cm$
Week $4$: $13\,cm$
Week $5$: $17\,cm$
Week $6$: $17\,cm$
Week $7$: $18\,cm$
Week $8$: $21\,cm$
Week $9$: $22\,cm$Write a formula to describe the correlation between the plant's height and the number of weeks.
So I'm really not understanding this assignment. There are several weeks where the plant doesn't grow. That means that I can't really say that $y = 2x + something$ because if that "something" for example was $4$, then yes it would be right on Week $0$ and Week $1$ ($2*0+4=4$ and $2*1+4 = 6$), but if we look at Week $2$ it's not right.
Can someone please explain to me how I should think when trying to solve these kind of assignments?
Edit: The same assignment also asks to calculate with the formula, how tall the plant will be at Week $14$.
I made a graph and simplified the line in order to get the formula that $y = 2x + 4$ where $y$ stands for the height of the plant and $x$ is the number of weeks. It's not that hard if you make the graph yourself and simply try to come up with the most optimal formula that you can achieve (remember, this assignment is ment for fourteen year olds, so you can't expect more than that).