Answer: Bonnie is correct
Reason:
The equation is t = 1.5p
The input p leads to the output t.
- p = number of pens
- t = total cost
The domain only cares about the input. It's the set of allowed inputs. Since p refers to a number of something, we can only work with whole numbers {0,1,2,3,4,...} which is why Bonnie is correct.
Unfortunately Buffy is incorrect because something like p = 2.7 isn't allowed in the domain. It's a real number, but not a whole number. It doesn't make sense to have a fractional or decimal amount of pens.