3/5 and 6/8 are not proportional as even though 3 goes into 6 evenly, 5 does not go into 8 evenly so that makes it disproportional.
You'll have to adapt this problem statement to Brainly, as Brainly does not have the Segment Tool available.
"starts with 90 pencils" implies that the y-intercept is (0,90).
"gives away 15 pencils" implies a slope of -15 pencils per unit of time
Thus, the # of pencils Jabian still has is P(x) = 90 - (15 pencils / time unit)x