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Answer:
(4) 750 < p < 1500
Explanation:
The total cost for p people is ...
c = 750 +2.25p
The average cost per person is this total divided by the number of people:
c/p = (750 +2.25p)/p
c/p = (750/p) +2.25
Natasha wants this to be between 2.75 and 3.25:
2.75 < c/2 < 3.25
2.75 < 750/p +2.25 < 3.25 . . . . . . use the expression for c/p
0.50 < 750/p < 1.00 . . . . . . . . . . . subtract 2.25
We can split this to two inequalities to find the limits of p.
Left one
0.50 < 750/p
0.50p < 750 . . .multiply by p
p < 1500 . . . . . . multiply by 2
Right one
750/p < 1
750 < p . . . . . . multiply by p
These bounds on p can be summarized as ...
750 < p < 1500 . . . . matches choice (4)
_____
Additional comment
Once you realize that the fixed costs will be divided by the number of people attending, the maximum cost you want ($1 more than the per-person charge) will set the minimum number of people. To have the $750 fixed cost contribute only $1 to the cost per person, there must be at least 750 people to share that cost. The only answer choice with a 750 person minimum is (4).