Explanation:
"the amount of sales" is in my understanding the earned money.
y = f(x) = the money earned.
x = number of bags sold.
so, y = f(x) just tells us how much money is earned, when x bags are sold.
and f(x) = 1.5x (whatever monetary unit is used)
650 bags are available.
the domain tells us the valid values for x.
so, what are valid numbers of bags of popcorn sold ?
well, if all goes bad, they sell no popcorn at all = 0 bags.
if all goes great, they will sell all 650 bags. but not more, because they have not more than these 650 bags.
so, the valid x values (domain) are whole numbers with
0 <= x <= 650.
whole numbers, because the problem description sounds like they would not sell parts of bags.
the range tells us the valid/expected intervals or sets of values for y (= the functional result values).
so, what are the possible amounts of money they can earn ?
for x = 0, also y = 0 (per y = 1.5x).
this is, where y starts. it cannot be lower than 0.
and then y grows with x with the factor of 1.5.
and the maximum amount of earned money we get, when x reaches the maximum (= all 650 bags are sold).
x = 650, y = 1.5×650 = 975
so, for the range we have
0 <= y <= 975
and y are rational numbers (due to the 1.5 factor)