Ella spent her whole allowance of $2.00, plus the 16¢ she had left over from last week, in bubble gum. If the pieces of gum had

Let x represent the quantity of pieces that Ella purchased.
Thus, the price for a single piece is calculated as 2.16/x
. If each piece cost a penny less, the price would be (2.16/x-0.01) for each piece. 
The equation will then be framed as (2.16/x-0.01)*(x+3)=2.16.

Next, we will work on solving this equation:


Upon solving for x, we find that x=24. Therefore, the answer is D.

Determining the answer here is quite straightforward. Ella has a total of $2.16, and we need to ascertain the cost per piece of gum.
It is known that if the gum cost one cent less, she would have acquired three more pieces.
 Currently, with 8 pieces priced at 27 cents each, a reduced price would allow her to have 8.64 pieces. This outcome, even after rounding, is incorrect as it does not yield 11.
 For 9 pieces at 24 cents each, a cheaper price would mean she could have 9.39 pieces, which still does not round to 12, indicating it's incorrect.
 At 16 pieces costing 13.5 cents each, at one cent less, she would acquire 17.28 pieces, which also confirms it's wrong because rounding does not yield 19.
 When purchasing 24 pieces at 9 cents each, with the cheaper price, she could buy 27 pieces, which is valid since 27-24 equals 3.
 Therefore, the correct answer is D) 24