A20-a18=a1+19d-a1-17d=2d =281-97
so
d=92
Find the rate of change, (y2-y1)/(x2-x1), from the data given...
(2.16-1.26)/(12-7)=0.18
(1.26-0.72)/(7-4)=0.18
Since the rate is constant, this is a linear equation of the form y=mx+b. Furthermore, since 0 pencils cost 0, b=0, so the cost of the pencils is simply the number of pencils times 18 cents...
c(p)=0.18p (cost with respect to pencils is 0.18 times the number of pencils)
We apply our knowledge in variation.
The solution can be seen in the photo
I’m pretty sure it’s 240 because you multiply then add
