Yeah i agree with him that is the correct answer.
That is the slope
rise/run
we see we have (2/5,1/2)
rise is y, run is x
(x,y)
((1/2)/(2/5)=(1/2)(2/5)=2/10=1/5
unit rate is y=(1/5)x
First you have to know how many pencils you could get with 1 dollar so divide 12 by 3 (thats 4 ) then, you do 4 times 4.50 (thats 18)