Answer:
18 is the number that would go in the green box 33/3 =11 and 54/3 = 18
19 < 30
Is that what you're looking for?
For easier, let's say x represents a pack of 10 and y represents a pack of 30
we can start with 2 of the 30's
2y=60
we can replace one of the 30's with 3 of the 10's
y+3x=60
and finally we can use all 10's
6x=60
there are only 3 ways
Checking, it all looks ok except for the range in number 7.
3 is a line with a slope so all reals (which you've written negative infinity to infinity, fine) make up both the domain and range.
4 is a parabola in the usual orientation, so a domain of all reals. There's a minimum so a range of y >= -1.