Since the graph is a straight line, its equation is of the form;
![y = mx + c](https://tex.z-dn.net/?f=y%20%3D%20mx%20%2B%20c)
Where m is the slope and c is the y intercept
We can use any two points on the straight line to find the value of m and c.
Let us use (0,30) and (4,150)
![m = \frac{150 - 30}{4 - 0}](https://tex.z-dn.net/?f=m%20%3D%20%20%5Cfrac%7B150%20-%2030%7D%7B4%20-%200%7D%20)
This simplifies to,
![m = \frac{120}{4} = 30](https://tex.z-dn.net/?f=m%20%3D%20%20%5Cfrac%7B120%7D%7B4%7D%20%20%3D%2030)
Let us substitute the value of m to obtain,
![y = 30x + c](https://tex.z-dn.net/?f=y%20%3D%2030x%20%2B%20c)
Substitute any of the points to find c. It is easier to use (0,30).
![30 = 30(0) + c](https://tex.z-dn.net/?f=30%20%3D%2030%280%29%20%2B%20c)
![c = 30](https://tex.z-dn.net/?f=c%20%3D%2030)
The equation of the graph now becomes,
![y = 30x + 30](https://tex.z-dn.net/?f=y%20%3D%2030x%20%2B%2030)
So in 10 weeks Ben will collect,
![y = 30(10) + 30](https://tex.z-dn.net/?f=y%20%3D%2030%2810%29%20%2B%2030)
![y = 300 + 30](https://tex.z-dn.net/?f=y%20%3D%20300%20%2B%2030)
![y = 330](https://tex.z-dn.net/?f=y%20%3D%20330)
Ben will collect 330 papers.
You can also use any two points to find the equation of this line.